At the beginning of the story the banker and several other people are having a discussion about whether the death penalty is a more humane form of punishment than life imprisonment. The banker argues that the death penalty is more humane because, unlike life imprisonment, it does not prolong the suffering of the criminal. One of the group, a young lawyer, argues vehemently against the banker and says that life imprisonment is much more humane than the death penalty because life is precious, and so any life at all is better than no life.
The banker seems affronted that anybody could challenge his view quite so passionately and so publicly, and to try and persuade the lawyer to back down, he says, "It's not true! I'll bet you two million you wouldn't stay in confinement for five years." The young man takes the bet but voluntarily raises the time period to fifteen years.
Later in the story, on the day before the fifteen-year period is due to expire, the banker realizes that he cannot afford to lose the bet. Fifteen years previously, when he made the bet, "his millions had been beyond his reckoning," meaning that he had more millions than he could count. Now, however, the banker is not so rich, and he stands to lose to the lawyer all the money that he has left. If the lawyer wins the bet, the banker now stands to lose everything and will be reduced to living "like a beggar." With this thought in mind, the banker decides that he must murder the lawyer before the bet can be won.