The banker makes a bet with a young lawyer that he can't last fifteen years in solitary confinement. If the lawyer does so, the banker will pay him two million rubles.
The lawyer is isolated for the fifteen years of his imprisonment in the banker's garden house. There, he reads many books.
When it becomes clear that the lawyer is going to win the bet because the fifteen years are almost up, the banker is in despair. He will be impoverished if he has to hand over two million rubles. He decides, therefore, to murder the lawyer. However, when he goes to do so, he finds that the lawyer has written a note saying he despises wealth and will leave five hours before his fifteen years is up in order to lose the bet.
When the banker reads the note, he begins to weep. We would think he is weeping for joy because he will neither have to commit murder nor lose his money. However, Chekhov tells us something different. The banker weeps from "contempt" for himself. He despises himself, we can assume (Chekhov doesn't tell us this), because he was ready to murder someone for money. All we are told, however, is that the banker later lies in bed unable to sleep because of his "tears and emotion." Rather than burn the lawyer's note, as we might expect, he keeps it in a fireproof safe. It is up to us as readers to decide what made it so precious to him.