When Myshkin meets Rogozhin on the train, Rogozhin is returning to Petersburg to claim his inheritance and lord it over his family.
He is also in love/lust with Nastasya.
Rogozhin meets Lebedev and makes him part of his regular drinking crew.
The day of Nastasya's birthday, Rogozhin crashes her visit to the Ivolgins and offers to outbid whatever money Ganya is bringing to the marriage, eventually bidding up to 100 thousand and promising to return with the money to her birthday party.
That night, Rogozhin and co. bust into Nastasya's party and he flings down 100 grand, showing up Ganya. Before Nastasya goes off with him, she pays a lot of attention to Myshkin, making Rogozhin suspicious and jealous of his new acquaintance.
For six months Nastasya goes back and forth from him to Myshkin.
When she leaves them both, he comes back to Petersburg.
Myshkin comes to visit him there, and Rogozhin shows him the copy of Holbein's "Christ in the Tomb" that he has hanging in his room. They exchange crosses with a blood-brothers type of promise.
A few hours later, Rogozhin attacks Myshkin with a knife and only doesn't stab him because Myshkin has a seizure.
Rogozhin skulks around Pavlovsk, keeping an eye on Nastasya and the rest of the gang. She has promised that as soon as Myshkin marries Aglaya, she will marry him.
He is there the night Aglaya comes to confront Nastasya, but is silent the whole time.
After Myshkin and Nastasya are engaged, he seems to disappear, although they still see his eyes in the crowd from time to time.
On the day of the wedding, Rogozhin appears just as Nastasya is about to get into the carriage, and she runs off with him.
He takes her to his house in Petersburg. There, he makes her enter the house as silently and secretly as possible, at the same time telling the servants lies to make them not suspect anything.
That night, he kills Nastasya in bed with his knife.
The next day, he finds Myshkin at his hotel and brings him back to the house to show him Nastasya's corpse.
The two men spend the night talking, and by morning Rogozhin has brain fever.
He is taken away by police, and when he recovers from brain fever two months later, Rogozhin gives a full confession of the murder, completely exonerating Myshkin. He is sentenced to fifteen years of hard labor in Siberia.