CHAPTER ONE
The Bet
Professor Augustus S. F. X. Van Dusen's appearance was as strange as his name. He was thin with the thin shoulders of a student and his face was extremely pale. His eyes were the eyes of a man who studies little things. They were always half-closed in concentration. Although he wore thick glasses you could see that his eyes were blue. But his strangest feature was his abnormally large forehead, on top of which sat a crown of yellow hair. Together all these things gave him a bizarre, almost grotesque personality.
Professor Van Dusen's family came from Germany. Many of his ancestors had been famous scientists; he was the logical result, the mastermind. And logic was his passion. He believed that two and two always equal four, except in unusual cases, when they may equal three or Five. He believed that all things that start must go somewhere, and he was able to concentrate all the mental force of his ancestors to solve any problem.
The public knew Van Dusen as The Thinking Machine and perhaps this phrase described him best of all. He spent all his time in his small laboratory where he invented brilliant theories that shocked scientists and had a profound effect on the world.
The Thinking Machine didn't have many visitors. When people did come to see him they were usually scientists. Two of these men, Dr Charles Ransome and Alfred Fielding visited him one evening to discuss some theory (what it was exactly is of no importance).
"That is impossible," said Dr Ransome.
"Nothing is impossible," said The Thinking Machine. "The mind is master of all things. When science understands this, it will be a great day."
"What about the airship?" asked Dr Ransome.
"That's not impossible at all," said The Thinking Machine. "It will be invented soon. I would do it myself, but unfortunately I'm too busy."
Dr Ransome laughed.
"I've heard you say things like that before," he said. "But they mean nothing. The mind may be master of the material world, but there are some problems that cannot be solved by thought alone."
"Give me an example," demanded The Thinking Machine.
Dr Ransome thought for a moment as he smoked.
"Well, what about the walls of a prison?" he replied. "No man can escape from a cell just by thinking about it. If he could, there would be no prisoners." He continued. "Let's imagine a case. A cell for prisoners who are condemned to death. These men will do anything to try to escape. Imagine you were in that cell. Could you escape?"
"Certainly," said The Thinking Machine.
"Of course," said Mr Fielding, "you could destroy the cell with an explosive, but if you are a prisoner inside the cell you can't have that."
"I don't need an explosive," said The Thinking Machine. "I would be just like any other prisoner and I would still be able to leave the cell."
"You could escape only if you entered it with tools," said Dr Ransome.
The Thinking Machine was visibly irritated.
"Lock me in any cell in any prison anywhere at any time, wearing only normal clothes, and I'll escape in a week," he declared. Dr Ransome was interested. Mr. Fielding lit a new cigar.
"You're saying that you could escape from the cell just by thinking about it?" Ransome asked.
"I could get out."
"Are you serious?"
"Certainly, I'm serious."
Dr Ransome and Mr Fielding were silent for a long time.
"Would you like to try it?" asked Mr Fielding finally.
"Certainly," said Professor Van Dusen and added ironically, "I have done more ridiculous things than that to convince men of less important facts."
Of course it was an absurd thing but they decided it at that moment.
"To begin now." said Dr Ransome.
"I'd prefer tomorrow," said The Thinking Machine, "because..."
"No, now!" said Mr Fielding. "You will be locked in a cell with no chance to communicate with friends. You will receive exactly the same attention as a real prisoner, a man condemned to death. Do you still agree to do it?"
"All right. Now, if you want," said The Thinking Machine, and he stood up. "The death-cell in Chisholm Prison?"
"Fine."
"And what will you wear?"
"Very little," said The Thinking Machine. "Shoes, long socks, trousers and a shirt."
"The guards will search you, of course."
"They must treat me like any other prisoner," said The Thinking Machine.
And so they made the arrangements. They had to obtain permission for the experiment but all three of them wore important men and everything was finalized with a few telephone calls. The prison governors could not understand why Professor Van Dusen wanted to do it. But one thing was certain. They had never had such an important prisoner.
The Thinking Machine dressed himself in the clothes that he was going to wear in prison, and called his housekeeper.
"Martha," he said, "it is now twenty-seven minutes past nine. I am going away. One week from tonight at half-past nine, these gentlemen and one or two others will have dinner with me here. Remember Dr Ransome likes carrots."
A driver took the three men to Chisholm Prison. The warden was waiting for them. He understood only that Professor Van Dusen was going to be his prisoner for one week. He was not a criminal, but he must be treated just like any other prisoner.
"Search him," said Dr Ransome.
The guards searched The Thinking Machine but they didn't find anything. The pockets of his trousers were empty and his shirt didn't have any pockets. They took off his shoes and socks and looked inside them. Nothing.
Dr Ransome regarded Van Dusen's weak body and his colorless face. He was suddenly sorry about his idea.
"Are you sure you want to do this?" he asked. 
"Would you believe me if I didn't do it?" The Thinking Machine replied.
"No."
"All right, I'll do it."
Ransome didn't like the arrogance in Van Dusen's voice. His sympathy for the man disappeared. He decided that the experiment was a good thing. It would teach The Thinking Machine a lesson.
"Will it be possible for him to communicate with anyone outside the prison?" he asked.
"No. It will be absolutely impossible," said the warden. "He will not have anything to write with."
"And the guards, will they send messages for him?"
"Not one word," said the warden. "They will tell me anything he says and they will give me anything he gives them."
"Good," said Mr Fielding.
"Of course if he does not escape in a week," said Dr Ransome, "and asks to leave, you will let him go?"
"I understand," said the warden.
Then The Thinking Machine spoke.
"I have three requests," he said, "I would like some toothpaste and also one five-dollar and two ten- dollar bills"
"Could he bribe your guards for twenty-five dollars?"
Not even for twenty-five hundred dollars."
"In that case, give him the money," said Mr Fielding.
"And what is the third request?" asked Dr Ransome.
"Could somebody clean my shoes?"
The three men looked very surprised. This last request seemed completely absurd, but they agreed to it anyway. After this, they took The Thinking Machine to his cell. They walked down a long corridor and stopped at the third steel door.
"Here is Cell 13," said the warden. "This is where condemned killers are kept. No one can leave it without my permission. No one in it can communicate with anyone outside. It is very near my office and I can hear any noise that comes from it."
"Is this cell all right, gentlemen?" asked The Thinking Machine.
"Yes, it's perfect," replied Fielding and Ransome together.
The guard opened the door and The Thinking Machine walked into the dark room. No sooner was he inside than the warden closed the door and locked it with a double lock. Ransome heard a noise from inside the cell.
"What is that noise?" he asked through the bars.
"Rats - the cell is full of rats," replied The Thinking Machine.
The three men said goodnight and were turning to go when The Thinking Machine called:
"What time is it exactly, warden?"
"Seventeen minutes past eleven."
"Thanks. I will see you all in your office at half-past eight one week from this evening," said The Thinking Machine.
"And if you do not?"
"There is no possibility of that."

CHAPTER TWO
Chisholm Prison
Chisholm prison was a large building. It was four floors high and stood in the centre of a large open space. The wall around it was six metres high and impossible to climb. Even if a man managed to escape from his cell, he could not pass over the wall.
The yard around the building was eight metres wide on all sides. This was the distance from the prison building to the wall. During the day, prisoners used the yard to do exercises. But it was not for those prisoners in Cell 13.
There were always four armed guards in the yard, one for each side of the building.
At night strong lights illuminated the yard and the wall. The wires that carried electricity to these lights ran up the walls of the building.
The Thinking Machine saw and understood all these things. He had to stand on his bed to see out of the small barred window. It was the morning after his incarceration. He soon realised that somewhere on the other side of the wall there was a river because he could hear the sound of a boat and saw a river bird in the sky. From the same direction he heard the sound of children playing baseball, so he knew that there was a children's playground between the prison wall and the river.
No man had ever escaped from Chisholm Prison and it was easy to see why. The walls of the cell were perfectly solid and the bars on the window were new. And in any case the window itself was too small to escape through.
But this didn't discourage The Thinking Machine. He looked up at the light and saw how the wire went from it to the wall of the prison building. He realised that the wire passed near the window of his cell. That could be useful.
Cell 13 was on the same floor as the prison offices. The Thinking Machine couldn't see the ground through the window of his cell. However, there were only four steps up to the office floor. Therefore the cell must be near the ground. Good.
The Thinking Machine remembered how he had come to the cell. First there was the outside guard's room which formed part of the wall, next to the prison gates. There was always one guard at these gates who let people come into the prison and then let them out again when the warden told him to. The warden's office was in the prison building. From the yard you had to pass through a solid steel door to get to it. The door had only one small hole in it to see who was there. Then between the office and Cell 13 there was a heavy wooden door and two steel doors in the corridors of the prison. Then, of course, there was the door of Cell 13.
"There are seven doors between Cell 13 and freedom," thought The Thinking Machine. "It will not be easy. But there are advantages. I am alone here. Nobody looks at what I am doing. 
There is one guard who brings my food three times a day, at six o'clock in the morning, at noon, then again at six in the afternoon.
And then there is the inspection at nine o'clock. But that is all."
There was nothing, absolutely nothing in his cell except a bed that was strongly made and impossible to dismantle. There was no chair, no table, no cup or fork or spoon. Nothing. The guard watched him while he ate and took away his plate and spoon as soon as he had finished.
The Thinking Machine considered all these facts very carefully. Then he began an examination of his cell. He examined the stones in the walls and roof and the cement between them. He walked over the floor many times but it was solid cement. After the examination he sat on his bed and thought for a long time. Because Professor Augustus S.F.X. Van Dusen had something to think about.
Suddenly, he was disturbed by a rat which ran across his foot and disappeared into a dark corner of the cell. The Thinking Machine looked hard into the corner. After some time he saw several pairs of yellow eyes looking back at him.
Then for the first time The Thinking Machine noticed the bottom of his cell door. There was a space of about five centimeters between the steel bar and the floor. The Thinking Machine walked into the corner where the rats were, but he continued to look at the door. The rats were afraid and tried to escape. There was the sound of running feet and several squeaks and then silence.
None of the rats had gone out the door, yet the cell was now empty. Therefore there must be another way out of the cell, even if it was very small. He got down on his hands and knees and began to look for the opening. Finally he found it. It was a small circular hole in the floor about four centimeters in diameter. "So this is how the rats escaped. Interesting." He put his hand in the hole. It seemed to be an old drainpipe.
The Thinking Machine sat on the bed and thought for an hour. Then he looked once more outside his cell window. One of the outside guards stood directly opposite, beside the wall. He was looking at the window of Cell 13 when The Thinking Machine's large head appeared. But the Professor didn't see the guard.
At twelve o'clock the Cell 13 guard brought The Thinking Machine his food. It was horrible but The Thinking Machine didn't mind. He wasn't interested in food. He spoke to the guard, who watched him as he ate.
"Have they made any modifications here in the last few years?" asked The Thinking Machine.
"Not really," said the guard. "They built the new wall four years ago."
"Have they done anything to the prison building?"
"Well, they painted the outside. And then seven years ago they had a new plumbing system installed."
"Ah, I see," said the prisoner. "How far is the river over there?"
"About a hundred metres. The boys have a baseball ground between the wall and the river."
The Thinking Machine had nothing more to say, but when the guard was ready to go he asked for some water.
"I get very thirsty here," he explained. "Could I have some water in a cup please?"
"I'll ask the warden," replied the guard, and he went away.
Half an hour later he returned with a small cup.
"The warden says you may keep this cup," he told the prisoner. "But you must show it to me when I ask for it. If you break it, I won't give you another one."
"Thank you," said The Thinking Machine. "I won't break it."
Two hours later the same guard was passing the door of Cell 13. He heard a noise and stopped. The Thinking Machine was on his hands and knees in a corner of the cell. There was the sound of several squeaks. The guard watched him.
"Ah, I've got you," he heard the prisoner say.
"What have you got?" said the guard.
"One of these rats," he replied. "See?" The guard saw a rat in The Thinking Machine's hands. The prisoner carried it towards the light. "It's a water rat," he said.
"Haven't you got anything better to do than catch rats?" asked the guard.
"It's terrible that there are rats in this prison," said The Thinking Machine. "Take this one away and kill it. There are many more where it came from."
The guard took the rat and killed it. Later he told the warden about the incident, but the warden only smiled.
Later that afternoon the armed guard in the yard outside Cell 13 saw the prisoner look out and put a hand through the bars of the window. Something white fell slowly to the ground. It was a roll of linen from a shirt, and wrapped around it was a five-dollar bill. The guard looked up at the window again but the face was no longer there.
With a smile he took the cloth and the five-dollar bill to the warden's office. There was something written on the outside of the cloth in strange ink. It said:
"Please deliver to Dr Charles Ransome."
"Ha!" said the warden, "His first plan of escape has failed. But why did he address it to Dr Ransome?"
"And where did he get the pen and ink to write with?" added the guard.
The warden looked at the guard and the guard looked at the warden. There was no easy solution to the mystery. The warden studied the writing carefully.
"Well, let's see what he wanted to say to Dr Ransome," he said. He unrolled the second piece of linen.
"Well, if that - what - what do you think of that?" he asked, extremely confused.
The guard took the piece of linen and read:
"Epa cseot d'net niiy awe htto n'si sih. T."

CHAPTER THREE
A Message from Cell 13
The warden spent an hour trying to discover what the message was. Why did his prisoner want to talk to Dr Ransome? And where had he got the materials to write? He examined the linen again. It was a part of a white shirt. But what had he written with? The warden knew that the prisoner didn't have a pen or a pencil. So what had he used? The warden decided to investigate. The Thinking Machine was his prisoner. "If this man is trying to escape by sending coded messages," he thought, "I will stop him."
The warden returned to Cell 13. He found The Thinking Machine on his hands and knees. He was catching rats. The prisoner heard the warden and turned to him quickly. 
"It's terrible," he said. "These rats. There are hundreds of them."
"Other men can live with them," said the warden. "Give me your shirt. Here is another one."
"Why?" demanded The Thinking Machine.
"You have attempted to communicate with Dr Ransome," said the warden, angrily. "As the warden of this prison, I must stop you." The Thinking Machine was silent for a moment.
"All right," he said, finally. "Here. Take it."
The warden smiled. The prisoner stood up and took off his shirt. He gave it to the warden. In exchange, the warden gave him a blue prison shirt. The warden looked at The Thinking Machine's white shirt. He compared the pieces of linen he had with the shirt. It was torn in two places. The Thinking Machine watched him.
"Did the guard give you those?" he asked.
"Yes, he did," said the warden. "And that is the end of your first attempt to escape." The Thinking Machine watched the warden as he looked at the shirt. He saw that there were only two pieces missing from it. He smiled.
"What did you write this message with?" asked the warden.
"I'm afraid you must discover that!" The Thinking Machine said.
The warden became angry but he didn't say anything more. He made a very careful inspection of the cell and the prisoner, but he found nothing. Nothing that The Thinking Machine could use as a pen. And the liquid that he had used to write the message was also a mystery. Finally the warden went out of the cell. He took The Thinking Machine's shirt with him.
"Well, he won't escape by writing messages on a shirt," the warden thought.
On the third day of his incarceration The Thinking Machine tried to bribe the guard so that he could escape. The guard brought his food and waited outside the cell door.
"The drainpipes of the prison go to the river, don't they?" The Thinking Machine asked.
"Yes," said the guard.
"I imagine they are very small?"
"Yes. They are too small to escape through."
There was silence. The Thinking Machine finished his food. Then he said:
"You know I'm not a criminal, don't you?"
"Yes."
"And I can leave the prison if I want to?"
"Yes."
"Well, when I came here I believed I could escape," said the prisoner. "Will you help me if I give you some money?"
The guard was an honest man.
"No," he said. 
"Five hundred dollars," said The Thinking Machine. "I am not a criminal."
"No," said the guard.
"A thousand?"
"No. If you gave me ten thousand dollars, I couldn't get you out. To get out you have to pass through seven doors and I only have the keys to two."
The guard ran to the warden's office and told him about the prisoner's offer.
"Plan number two fails," said the warden and smiled. "First a message and then a bribe."
At six o'clock, the guard went to Cell 13 again to bring food to The Thinking Machine. He stopped in the corridor. There was a noise coming from inside the cell. The guard walked very quietly to the cell door. Through the bars he saw The Thinking Machine at the window. He was trying to cut through the iron bars of the window with a file. 
The guard went back to the office and told the warden. The two men went back to Cell 13, walking very quietly. The warden looked into the cell and saw The Thinking Machine still at the window. He entered the cell.
The Thinking Machine turned round and jumped onto the floor. He tried to hide the file in his hand.
"Give it to me," said the warden.
"No," said the prisoner. There was anger in his voice.
"Come on. Give it to me."
"No," repeated The Thinking Machine.
"Very well. Search him," said the warden to the guard.
The guard searched The Thinking Machine. After some minutes he found a piece of steel about five centimeters long in the prisoner's trousers. A few minutes later he found another piece. The guard gave the pieces of steel to the warden. The warden looked at them.
"You couldn't cut through the bars on the window with these," he said.
"Yes I could," said The Thinking Machine.
"In six months perhaps," said the warden, smiling.
"Just wait, you'll see," said The Thinking Machine.
Once more the guard searched the cell. But once more they found nothing. The warden stood on the bed and looked at the bars of the window. He took the bars in his hand and tried to move them. They were immovable. He smiled and then got down from the bed.
"Forget it, Professor, you will never escape from here," he said.
The Thinking Machine said nothing. He just sat on the bed with his head in his hands. The warden and the guard went out of the cell and closed the door. 
"He is mad to try and escape," said the warden, "but he is very clever. I would like to know what he used to write that coded message."
It was four o'clock the next morning when a terrible scream resounded through the prison. It came from a cell near the centre of the building, a sound full of horror and great fear. The warden heard it and ran with three of his men into the long corridor that went to Cell 13.

CHAPTER FOUR
A Strange Voice
As they ran they heard the scream again. The white faces of prisoners appeared at cell doors. They were afraid.
"It's that crazy man in Cell 13." the warden said.
He stopped and looked into the cell. "That crazy man in Cell 13" was sleeping comfortably in his bed. They heard the scream again. It was coming from somewhere above. The warden and the guards went upstairs. There they found a man in Cell 43, directly above Cell 13. He was sitting in the corner of his cell like a child.
"What's wrong?" demanded the warden.
"Thank God you've come!' said the prisoner.
"What is it?" demanded the warden again.
He opened the door and went into Cell 43. The prisoner's face was white with terror.
"Take me out of this cell, please take me out," he said.
"What is it?" asked the warden.
"I heard something - something."
"What did you hear?"
"I can't tell you," said the prisoner. "Please take me out of this cell - put me anywhere - but take me out of here."
"Who is this man?" the warden asked the guard.
"His name is Joseph Ballard," the guard replied.
"And what is his crime?"
"They say he killed a woman with acid."
"But they can't prove it," said the prisoner. "They can't prove it!" The warden was silent for a minute. 
"Listen to me, Ballard," he said, finally. "If you heard something, I want to know what it was. Now tell me."
"I can't tell you." Ballard was crying now. "Where did it come from?"
"I don't know. Everywhere - nowhere. I don't know."
"Was it a voice?"
"I can't tell you," said the prisoner. "You must tell me," said the warden, angrily.
"It was a voice - but - but - it wasn't human," said the prisoner.
"A voice, but not human?" repeated the warden. He was confused.
"It was strange and very far away, like a ghost."
"Did it come from inside or outside the prison?"
"It didn't come from anywhere. It was here, there, everywhere. I heard it. I heard it!"
For an hour the warden tried to get the story, but Ballard became silent and didn't say anything more. Finally the warden went away. He was very confused. Ballard sat at his cell door until morning, his white face staring through the bars.
It was the fourth day of The Thinking Machine's incarceration. He stood at his cell window and threw another piece of linen to the guard outside. And once more the guard took it to the warden. The warden read the message on it. It said:
"Only three days more."
The warden was not surprised by the message. He knew The Thinking Machine meant that there were only three days more before he escaped.
"But how did he write it?" the warden thought. "Where did he find another piece of linen? Where? How?" He looked at the linen. It was white, like the material from a shirt. He took The Thinking Machine's shirt and put the two original pieces of linen on the torn places. The third piece was completely superfluous. But it was the same material. "Where did he get it? And where - where does he get anything to write with?"
Later on the fourth day The Thinking Machine spoke to the guard outside his window.
"What day of the month is it?" he asked.
"The fifteenth."
The Thinking Machine made a mental astronomical calculation. "Good," he thought. "Tonight the moon will not rise before nine o'clock." Then he asked another question.
"Who looks after the big lights on the roof?"
"An electrician from the company."
"You have no electricians in the building?"
"No."
At the end of the afternoon, just before he finished work, the outside guard saw The Thinking Machine's head again at the window. He had something in his hand which he threw to the ground. It was a five-dollar bill.
"That's for you," said the prisoner.
Once again, the guard took it to the warden.
"He said it was for me."
"I imagine it's a present from him. I think you can accept it," said the warden. Then suddenly he stopped. "Wait a minute. When the professor went into the cell he had one five-dollar bill and two ten-dollar bills. There was a five-dollar bill with the first message. I have it here. But now he has given you another five- dollar bill. It's impossible. He has only two ten-dollar bills."
"Perhaps somebody changed a ten-dollar bill for him," said the guard.
"Perhaps. But tonight we are going to search Cell 13 again. We are going to search it as no cell has ever been searched before."
So that night at three o'clock in the morning the warden and his guards searched The Thinking Machine's cell again. The warden found the hole in the floor. He put his hand into it. There was something there. He pulled it out. A dead rat. He threw it to the floor in disgust. But he continued the search. Once more he examined the bars on the window but found them to be solid. He then examined The Thinking Machine's clothes. In his trousers he found some money.
"Five one-dollar bills!" said the warden. He was very surprised.
"That's right," said the prisoner.
"But the... you had two tens and a five... how do you do it?"
"That's my business," said The Thinking Machine.
"Did any of my men change this money for you?"
"No."
"Well, do you make it?" asked the warden.
"That's my business," said the prisoner again.
The warden was very angry. He left the cell and went back to bed.
About an hour later he heard the scream again. He got up and ran immediately to Cell 43, where he saw Ballard, his face pressed against the bars of the door.
"Take me out, take me out," he screamed. "I did it. I did it. I killed her. Take me out of here."
"Was it the voice again?" asked the warden.
"Yes," said Ballard.
"What did it say?"
"Acid - acid - acid!" said the prisoner. "It knew. I threw the acid in the woman's face and killed her. Oh!"
"Acid?" repeated the warden, more confused than ever.
CHAPTER FIVE
Countdown to Freedom
On the fifth day of The Thinking Machine's incarceration, the warden looked tired. He wanted this thing to finish. He wanted his confusion to end. But that day The Thinking Machine threw another piece of linen to the guard. It said "Only two days more". This time there was a silver half-dollar with it.
Now the warden knew - he knew that the man in Cell 13 didn't have any half-dollars - he couldn't have any half-dollars. Just as he couldn't have pen and ink and linen. But he did have them. It was a fact, not a theory. And that is why the warden looked so tired.
Then there was the voice that Ballard had heard. The word acid. It didn't mean anything, of course. Ballard was obviously mad. But there were so many things that "didn't mean anything" now that The Thinking Machine was in the prison.
On the sixth day, the warden received a letter from Dr Ransome. It said:

Dear Sir.
Mr Fielding and I will meet you in your office tomorrow evening. If Professor Van Dasen has not escaped - and we believe he has not because we have not received a letter from him - we will meet him there too.
Yours, Dr Ransome.

That day The Thinking Machine had three more messages for the warden. They were written on the same linen and referred to the meeting with Dr Ransome and Mr Fielding.
On the afternoon of the seventh day the warden passed Cell 13 and looked in. The Thinking Machine was sleeping on his bed. Everything in the cell was completely normal. "He cannot escape between now and half-past eight this evening," the warden thought.
That evening after six o'clock he saw the guard. "Is everything all right in Cell 13?" he asked. "Yes sir," replied the guard. "But he didn't eat much today." The warden was feeling happy when he met Dr Ransome and Mr Fielding that evening, at seven o'clock. He wanted to show them The Thinking Machine's messages. He wanted to tell them about the events of the week. But before he could speak, the guard from the river side of the prison yard came into the office.
"The light on my side of the yard is broken," the guard said. Oh no. Another problem," said the warden. The guard returned to his post in the dark. The warden called the electric light company.
"Hello. This is Chisholm Prison," he said into the phone. "One of our lights is broken.
Could you send four men here to repair it? Thank you. Goodbye." The warden went out into the yard. While Dr Ransome and Mr Fielding were waiting, the guard from the prison gate came into the office. In his hand was a letter. Dr Ransome looked at the letter.
"Incredible!" he said. "What is it?" asked Mr Fielding. The doctor gave him the letter. Fielding looked at it. "It's a coincidence.  It must be," he said. It was almost eight o'clock when the warden returned to his office.
"The electricians have arrived," he said. "They are working on the light now."
The warden telephoned the guard at the prison gate. "How many electricians came in?" he asked. "Four," was the reply.
"All right. You must be certain that only four men go out of the prison," said the warden. He put down the phone and took the letter.
"My God! It's not possible," he said, shocked.
"What is it?" asked Mr Fielding.
"It's a letter from Cell 13," said the warden. "An invitation to dinner!"
"What?" said Ransome.
The three men were silent for a long time. Finally the warden called a guard.
"Go down to Cell 13 immediately," he said, "and see if the Professor is still there."
The guard ran down the corridor. Dr Ransome and Mr Fielding examined the letter.
"It's Van Dusen's handwriting; there's no doubt about that," said Dr Ransome. "I've seen too much of it."
At that moment the telephone rang again. It was the guard at the prison gate. There were two newspaper reporters and they wanted to see the warden. The warden told the guard to let them come in.
"It's impossible," he said. "Professor Van Dusen must be in Cell 13."
Then the guard returned.
"He's still in his cell, sir," he said. "I saw him. He's sleeping."
"There. I told you." said the warden. "But if he is still in his cell how did he send the letter?"
There was a knock at the door.
"It's the reporters," said the warden. "Come in."
The door opened and the two men entered.
"Good evening, gentlemen," said one. It was Hutchinson Hatch. The warden knew him well.
Then the second man came in.
"Well, I'm here," he said. It was The Thinking Machine.
The warden sat with his mouth open. He was paralyzed.
"How - how - how did you do it?" asked the warden, finally.
"Let's go back to the cell," said The Thinking Machine.
The men walked down the corridor to the door of Cell 13.
"Look inside," said The Thinking Machine.
The warden looked inside. Everything looked normal and there - there on the bed was the figure of The Thinking Machine. Certainly! There was his yellow hair! The warden looked again at the man beside him. "I must be mad," he thought.
Then he unlocked the cell door and The Thinking Machine went inside.
"Look here," he said.
He put his foot on the steel bars at the bottom of the cell door and three of them fell out.
"And here, too," The Thinking Machine stood on his bed and put his hand to the bars on the window. All of them came out.
"So what's this in the bed?" asked the warden.
"It's a wig," The Thinking Machine replied. "Take the cover off."
The warden did this. Under it was a coil of strong rope about ten metres long, a knife, three files, three metres of electric wire, a pair of steel pliers, a hammer and a pistol
"How did you do it?" asked the warden. "You gentlemen have an invitation to dinner with me at half-past nine," said The Thinking Machine. "Come on, or we shall be late."
"But how did you do it?" the warden insisted.
"You cannot hold a man in prison who can use his brain," replied The Thinking Machine. "Come on, or we shall be late."

CHAPTER SIX
How Did He Do It?
When dinner was finished The Thinking Machine turned to Dr Ransome.
"Well, do you believe me now?" he asked.
"Yes I do," replied Dr Ransome.
There was a long silence. Like all the other guests, Ransome was waiting for the explanation.
"So, tell us how you did it," said Fielding, finally.
The Thinking Machine began the story.
"The agreement was to go into a cell in Chisholm Prison with nothing but the necessary clothes and to leave that cell within seven days. I didn't know Chisholm Prison. When I went into the cell I asked for three things: toothpaste, two ten-dollar bills and one five-dollar bill and to have my shoes blacked. You agreed to these things.
"I knew that there was nothing useful in the cell, so I had to use these three innocent things to help me escape. But anything is dangerous in the hands of a man like me.
"The first night I did two things. I slept and I ran after rats. You gentlemen thought I wanted time to organize an escape with assistance from outside the prison. But this was not true. I knew I could communicate with anyone I wanted to at any time."
The warden looked at him for a moment. The Thinking Machine continued.
"The guard woke me up at six o'clock the next morning. He brought me my breakfast. He told me lunch was at twelve o'clock and dinner was at six. I knew that between these times I was alone. So after breakfast I examined the outside area from my cell window. I saw that it was impossible to get over the wall. But I knew that on the other side of the wall there was a river and also a playground. The guard confirmed it. So I knew one important thing. A person could come near the prison on that side without attracting the attention of the guards.
"But there was something even more important. I saw a wire which went to the light on the prison roof. It was very near my cell window. I knew then that if it was necessary I could cut off that light.
"Then I thought about escaping through the prison building. I remembered the way to my cell. I knew that was the only way out. There were seven doors between my cell and the outside. It was too difficult."
The Thinking Machine stopped for a moment. Dr Ransome lit a new cigar. For several minutes there was silence. Then The Thinking Machine continued.
"When I was thinking about these things a rat ran across my foot. It gave me a new idea. I saw there were at least six rats in the cell. But they didn't come from under the door. I ran after them and they disappeared. But they didn't go out of the door. So I knew there was another way out.
"I looked for this other way and found it. It was a hole in the floor. It went to an old drainpipe. Obviously the rats came this way. But where did they come from? Drainpipes normally go outside the prison. This one probably went to the river or near it. So the rats came from that direction.
"When the guard came with my lunch he told me two important things. One was that there was a new plumbing system in the prison. The other was that the river was only a hundred metres away. So I knew that the pipe in my cell was part of an old system. And I knew it went to the river. The other end of the pipe was outside the prison walls. 
"But before I could start work, I knew I had to distract the warden. I wanted him to think that I was trying to communicate with you, Dr Ransome. So I took two pieces of linen from my shirt and wrote a message on them. Do you have the message, warden?"
"Yes." The warden looked at the codec message. "But what does it mean?" he asked. "Read it from right to left, beginning with the T" said The Thinking Machine. "Don't consider the division into words."
The warden read the message.
"T-h-i-s," he began, "is not the way I intend to escape." The warden smiled. "But what did you write it with?"
"This," said The Thinking Machine. He put his foot on the table. On it was the shoe that he wore in prison. But the polish was gone.
"The shoe polish, mixed with some water, was my ink," said The Thinking Machine, "and the metal end of the shoe lace was a good pen."
The warden laughed. "Continue," he said.
"After the message the warden wanted to search my cell. This was good. I wanted him to search my cell very often. I thought, 'He won't find anything so he will stop and leave me alone.'
"The warden took my shirt away and gave me a prison shirt.
Without my white shirt I couldn't write any more messages. But I had another piece of the same shirt in my mouth."
"Where did it come from?" asked the warden. "I saw that there were only two pieces cut from the shirt. And I had both of them."
"You forget that shirts like mine have three layers of linen," The Thinking Machine replied. "I took out the inside one. You didn't notice it.
"Now that the warden was busy, I started to work on my real escape plan. I knew that the pipe from my cell went to the playground outside the prison. It is a place where boys play baseball. I knew many of the boys there. I knew that the rats came into my cell from out there. Perhaps it was possible for me to communicate with someone outside. I could use the rats.
"The first thing I needed was a long thread. So I used the thread from my socks." He pulled up his trouser-legs. The strong thread at the top of his long socks was not there.
"Then on one half of my last piece of linen I wrote a message for Hutchinson Hatch. He is a friend and often helps me. I knew he would help me this time. It was a great story for his newspaper. I tied a ten-dollar bill to the letter to attract attention. People always find money. I wrote on the linen: 'If you find this message give it to Hutchinson Hatch. He will give you another ten dollars for the information.' Then I wrote instructions for Hatch.
"I had to get this note outside the prison. There were two ways but the best way was the rats. I took one of them. I tied the linen and the money to one of its legs and tied my thread to another. Then I put it in the pipe.
"From the moment the rat disappeared into that dirty pipe I was nervous. The thread could break. Anything could happen. I waited. I was holding the thread and I saw that it became gradually shorter. Finally there was only about one metre of thread in my hand. I knew that the rat was outside the prison. But would Hatch receive the message?
"I had to wait. I decided to try some other man oeuvres. This was to confuse the warden more. I tried to bribe the guard. I tried to cut through the bars on my cell window. The warden became very angry. He took the bars in his hands to see if they were solid. They were - then.
"That night I didn't sleep. The thread was tied to my hand. I waited for the signal from outside. I thought. 'If Hatch has received the message, and if he finds the drainpipe, he will pull the thread.' At half-past three in the morning I felt something pull the thread."
The Thinking Machine turned to Hutchinson Hatch.
"Now you can explain what you did," he said.
"A small boy brought the linen message to me. I gave the boy another ten dollars. I got some string and then some wire. I went with the boy to the playground. I looked for the end of the drainpipe for an hour. Then finally I found it. It was about thirty centimeters in diameter. I took the end of the thread and pulled it three times. The Professor pulled twice to reply. Quickly I tied my string to the Professor's thread. Then I tied the wire to the string. Professor Van Dusen began to pull it all into his cell. The wire was the most important because it could not break. The thread was too weak. It could break easily. With the wire I could transport things to the cell."
"Yes," continued The Thinking Machine. "I was very happy when the wire arrived in the cell. Then we tried another experiment. I spoke to Mr Hatch through the pipe. He heard me but it was not easy for him to understand me. I wanted some nitric- acid and I had to repeat the word 'acid' several times. Then I heard a scream from the cell above me.
"With the wire it was easy to transport things to my cell. And it was also easy to hide them. I could put them into the pipe. You, Mr Warden, found the pipe but you could not find the wire. Your hands are too big. My fingers are longer and thinner so it was easy for me. In addition I put a dead rat in the pipe. You pulled it out."
"I remember," said the warden.
"The rat was there to stop you investigating the pipe," said The Thinking Machine.
"That night Mr Hatch could not send me anything useful. But he did send me change for ten dollars as a test. The next clay I continued to work on my plan.
"For this it was necessary that the guard outside saw me often at my cell window. To attract his attention I threw messages to him. I stood at my cell window for hours. Sometimes I spoke to him. He told me that there were no electricians inside the prison. If there was a problem with the lights they had to call the light company.
"This was perfect for my escape plan. There was only one more thing to do before I escaped. Once again I spoke to Mr Hatch through the pipe. It was the fourth night of my incarceration. Again Mr Hatch could not understand me. Again I repeated the word 'acid' three times. It was this that made the prisoner above me confess to murder. The guard told me the next day. The prisoner heard strange voices through the pipe. He thought it was a ghost.
"With nitric acid it was very easy to cut the bars of the window. But it was a long process. The outside guard saw me standing at my window. He didn't know what I was doing. As he watched me I cut the bars with a piece of wire covered with acid. On the night of my escape I used the same acid to cut the electric wire that went to the lights. The yard outside my window was completely dark. It was easy to escape.
"I also had a wig from Mr Hatch. It was the same color as my hair. Yellow. I put it in the bed with some other things that Hatch sent me. When the guard passed the door he thought I was sleeping."
"But how did you get outside the prison gate," asked the warden.
"It was simple," The Thinking Machine replied. "As I said. I cut the wire to the lights before the guards turned on the current. When they turned on the current, the light on my side of the yard didn't work. The outside guard went to your office to tell you and I escaped through my cell window. I stayed in the shadows until the four electricians arrived. Mr Hatch was one of them.
"When I saw him he gave me some workman's clothes to put on. You, Mr Warden, were standing only three metres away. Then Mr Hatch called me - as a workman - and together we went out of the gate to get something from the van. The guard at the gate knew that there were four workers in the yard. He saw that we were workers so he let us go out of the prison. Then we changed clothes and came back in. We went to your office and asked to see you. That's all."
"And the letter of invitation?" asked Ransome.
"I wrote it in my cell with Mr Hatch's pen," said The Thinking Machine. "Then I sent it through the pipe and Mr Hatch posted it."
There was silence for several minutes. Dr Ransome was the first to speak.
"Incredible!" he said. "Absolutely brilliant!"
But Mr Fielding had two more questions.
"And what was the toothpaste for?" he asked.
"For brushing my teeth."
"Why did Mr Hatch come with the electricians?"
"His father is the manager of the company," said The Thinking Machine.
"But what if there was no Mr Hatch outside to help you?"
"Every prisoner has at least one friend who will help him if he can."
"What if there was no old drainpipe in your cell," asked the warden.
"There were another two ways to escape," said The Thinking Machine.
Ten minutes later the telephone rang. It was for the warden.
"Is the light working now?" asked the warden through the phone. "Good. The wire was cut beside Cell 13? Yes I know. What's that? There are too many electricians. Two went out of the prison and there are three still inside. But only four men came from the light company."
The warden turned to the others, confused.
"The guard says that he saw four electricians come into the prison. Two went out again. But there are still three men inside," he said.
"Don't you remember? I was the extra man," said The Thinking Machine.
"Oh," said the warden. "I see." He turned back to the phone. "You can let the fifth man go. He's all right."

- THE END -
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