The protagonist of the story is a former colonel of military counterintelligence named Nikolai Ustuzhanin. A principled man, he always acts according to his own principles, but is also capable of spontaneous decisions. Sometimes he is willing to act to his own detriment in order to achieve his goals. During an operation in which he is involved, an agent is killed, and as a result, Nikolai is suspended from further work. The colonel believes that there is a traitor among his colleagues. He is determined to find out who is behind it at any cost.