After leaving Lebedev's house, Prince Myshkin goes to visit Rogozhin, whose house he very dark and dismal. Rogozhin opens the door and invites the prince inside. After remarking how similar the dark house is to Rogozhin's lifestyle, Myshkin tells him that he does not intend to interfere with his relationship with Nastassya Filippovna. If she decides to run from Rogozhin herself—which is what happened in Moscow—Myshkin will take her in. The prince does not hide his opinion that a marriage between Rogozhin and Nastassya Filippovna would result in mutual destruction. Myshkin loves her with pity and is also fond of Rogozhin himself.

Rogozhin tells Myshkin that Nastassya Filippovna has cheated on him; for this, he once beat her severely. Afterward, he refused to eat or drink until she forgave him. The prince tells Rogozhin that Rogozhin's love for Nastassya Filippovna is very close to hatred and that if the two ever got married, he would not forgive her for all the suffering she has caused him. Hence, Myshkin says he cannot understand why she is marrying Rogozhin. Rogozhin responds that she is doing so precisely because she knows that he will most likely kill her; she is really in love with Myshkin, but she feels she cannot marry him because she does not want to ruin his life.

Before Myshkin leaves, he notices a large garden knife hidden inside one of Rogozhin's books. As Rogozhin escorts the prince out, they pass by a painting by Holbein, of a Christ who has just been taken off the cross. Myshkin cannot help but stare at this painting for a long time; Rogozhin asks him if he believes in God. In response, the prince tells four stories, the fourth of which explains the essence of religion as he understands it. The story is of a young mother delighting in her newborn. The prince thinks that God feels joy in his creation much as the mother feels joy in her child. Myshkin and Rogozhin then exchange crosses, and Rogozhin takes the prince to his mother, who blesses the prince.

After Myshkin leaves Rogozhin's house, he goes to visit the Yepanchins. Not finding them at home, he leaves his card. He then decides to go to Kolya's hotel, but the boy is not there. After waiting for Kolya for several hours, Myshkin goes wandering about the city. He buys a train ticket to Pavlovsk to see Aglaya, but then suddenly changes his mind and leaves the train station. He is in a state of great agitation and emotional anxiety. His mind wanders from subject to subject. He thinks of what his epileptic fits are like. He describes them as a momentary glimpse of utter clarity before his mind is plunged into darkness.

Myshkin is then overcome with a desire to see Nastassya Filippovna. Acting contrary to what he promised Rogozhin, he goes to the house where she was staying in St. Petersburg. She is not at home, so the prince leaves his name with the maid who opens the door. As he starts walking back, he notices Rogozhin on the other side of the road, but pretends not to see him. Myshkin returns to the hotel, increasingly closer to experiencing a fit of epilepsy.

As the prince mounts the stairs, he sees Rogozhin, who is about to stab him. At that instant, however, Myshkin's body contorts as he finally experiences an epileptic attack. Rogozhin runs, and the prince falls down the stairs. Luckily, Kolya received the note Myshkin left him, and the boy comes to the hotel. Kolya recognizes the prince and makes sure he is taken to his room, where a doctor soon arrives to see him. Myshkin and Kolya then go to Lebedev's house. In three days, all of them are in Pavlovsk.