The story starts with the old banker remembering a party he had thrown 15 years ago. The party guests included many intellectuals and clever men who engaged in various interesting conversation, eventually landing on the controversial topic of the capital punishment. Most of the guest disapproved of the death penalty and thought it was immoral and that it should be replaced by the imprisonment for life. The banker objected to this idea, arguing that the death penalty is more humane and moral because it grants the man a quick death as opposed to the imprisonment for life, which kills him slowly. Other guest suggested that both methods are equally immoral because they both attempt to take a life and that is something the State has no right to do as it is not God.
Among the party guests was also a young lawyer who when asked a question about his opinion answered that he sees both punishments equally immoral, but if he had to choose he would certainly pick the imprisonment for life as living in confinement is better than not living at all. This idea spurred a lively discussion, and the banker (who was much younger back then) was suddenly carried away with excitement. He declared it is not true and bet the lawyer two millions he wouldn't be able to stay in solitary confinement for period of 5 years. The young lawyer accepted the bet and added that he will not stay 5 years but 15 years.
Later in the evening it was decided that the lawyer would spend the time of the imprisonment in the lodge in the baker's garden. They agreed that for 15 years this man would not be allowed to leave the lodge, to see or hear people, or to receive letter and periodicals. What he was allowed to do was to read books, write letters, to drink, and to smoke. In the lodge there was a little window through which he was to conduct any sort of relations with the outer world. During his confinement he firstly started to suffer of depression of loneliness, however, with time he started studying vigorously and we can see him developing constantly throughout the story. In the course of 4 years the lawyer manages to read six hundred volumes regarding various topics from classic literature through science to philosophy. In the final years of the imprisonment he studied chemistry and medicine, but also spend time reading Byron and Shakespeare.
In the mean time, the banker gambled most of his fortunes and could not decide which were bigger, his debts or his assets. He realized that only thing that can save him from having to pay the two millions was the death of the lawyer. One day before the period of the confinement concluded, the banker decided to kill the prisoner. He found him in his cell asleep and noticed a note on the table. In the note the lawyer declared that during the imprisonment he came to hate all the material and therefore renounced his reward. The banker was overjoyed. He kissed the lawyer on the forehead and left happy that he did not have to kill anyone. The next day the warden reported that the prisoner left the lodge through the window and disappeared.