Professor Augustus S. F. X. Van Dusen, the main character in Jacques Futrelle's "The Problem of Cell Thirteen," is often called "The Thinking Machine." Challenged by two friends, the professor determines to prove his claim that in seven days, he can escape from the strongest, most heavily guarded cell at Chisholm Prison.
The professor does indeed escape. He sends a message to reporter Hutchinson Hatch through the drainpipe in his cell, and Hatch sends back through the pipe all the professor needs, including materials to cut the bars on his cell window and the electric wire on the wall outside his cell. When an arc light goes out due to the cut wire, the warden calls in the electric company to fix it. Four company men enter the prison yard. One of them is Hatch (for his father manages the company).
The professor has already climbed out his window and is waiting on the ledge when the workmen enter. He quickly dresses in the clothing Hatch has brought him and poses as a fifth workman. The professor and Hatch leave the prison yard with the excuse that they need something from the wagon. They change their clothing and re-enter the prison as two reporters.
Meanwhile, three electricians are left in the yard to fix the light. The professor reveals his identity to the shocked warden. A while later, the professor, his two friends, Hatch, and the warden gather at the professor's house for a meal and an explanation of the professor's escape. At the end of the meal, the warden receives a call from the prison. The guards are puzzled. They know that four electricians entered and two left, but there are still three in the yard. Where did that fifth man come from? And what should they do about him?
The professor quickly remarks, "I was the odd one," and the warden tells the bewildered guard, "Let the fifth man go. He's all right." That "extra" electrician probably breathes a sigh of relief!