The banker is supposed to give his two million rubles to the lawyer as prize money for successfully completing the bet of living fifteen years in solitary confinement. In order to avoid parting with his money next day, he decides to murder the lawyer. In the darkness of night, he stealthily enters his cabin in order to strangulate him to death.
Soon he discovers that he doesn't need to kill the lawyer because the lawyer is no more interested in the prize money. In a letter he has written,
To deprive myself of the right to the money I shall go out from here five hours before the time fixed, and so break the compact.
Instead of going mad with happiness knowing that he no more has to commit the crime of murder to keep his money to himself, the banker is filled with tears. He rather spends hours weeping on his bed. His tears are not of joy but of self-contempt. The way the banker reacts is unexpected of him. The fact that the wealthy and corrupt banker spends a restless night weeping bitterly out of guilt and self-reproach is the change that has occurred to the banker.
At no other time, even when he had lost heavily on the Stock Exchange, had he felt so great a contempt for himself. When he got home he lay on his bed, but his tears and emotion kept him for hours from sleeping.
The banker’s realization of his spiritual degradation to that of a monster and the lawyer’s elevation to sainthood effects this change in him.
He knows it very well that his money is ill-gotten. He has no record of how much of it he has already lost in gambling and self gratification. He finds it too hard to part away with his two million rubles. The only way that to avoid this is to eliminate the lawyer, he thinks. He plans to do so in a way that the suspicion would fall on the watchman.
The lawyer, on the other hand, has acquired great wisdom and spiritual knowledge during his solitary confinement. No longer does he wish to acquire material wealth for self-indulgence. When the banker sees the lawyer's spiritual progress, he finds himself fallen to such a low state that he is overwhelmed with a sense of self reproach. This is what brings the change in him.