Prince Myshkin comes to Petersburg and stumbles into Rogozhin, and the Ivolgin and Epanchin families. They are all trying to figure out what to do with Nastasya Philipovna, a beautiful woman without a proper place.
Myshkin's innocence and sense of duty makes him propose to Nastasya, thus making enemies of other potential suitors, and complicating his budding relationship with Aglaya. He abandons everything to try to help Nastasya in whatever way he can, eventually asking her to marry him.
The wedding is interrupted when Nastasya runs off with Rogozhin, who then takes her back to his house in Petersburg and kills her. Myshkin finds him and the corpse, and after a tense and horrible night, becomes yet again almost catatonic.