Having left Switzerland, Prince Lev Nikolayevich Myshkin returns to St. Petersburg. The man is twenty-six years old, the last member of a noble family, for he was orphaned early in childhood. Suffering from severe nervous disease, he was sent by his guardian, Pavlishchev, to the Swiss resort. After four years, he returns home. He encounters Parphen Rogozhin on his way. The acquaintance mentions Nastasya Filipovna’s name, mistress of a wealthy aristocrat Totskii, and the woman is in love with.
Upon arrival he pays a visit to General Yepanchin, whose wife is his distant relative. The family has three daughters: the elder Alexander, Adelaide and younger, the overall favorite and pretty, Aglaia. Prince affects everyone with his spontaneity, credulity, frankness and naiveté, so extraordinary that at first he is taken very cautiously, but with great curiosity and sympathy. Here he meets an extremely proud Secretary of the General, and sees the portrait of Nastasya Filipovna. Her proud beauty and hidden suffering affect him deeply.
Soon some details are clarified: Totskiy, trying to get rid of Nastasya and hatching plans to marry one of the Yepanchin’s daughters, wants Gan Ivolgin to marry her and promises him seventy-five thousand as dowry. Gan wants this money. With its help, he can become a part of high society. But he would prefer to marry Aglaia. He is waiting for her final word. The prince becomes the unwitting intermediary between Aglaia and Gan.
Meanwhile Lev is offered to live in the Yepanchins’ apartment. Hardly he has granted his room and got acquainted with all the inhabitants of the apartment as two unexpected events occur. Nastasya visits the house to invite Gan and others to her evening. She amuses herself by devouring general Ivolgina’s fantasies that only heat up the atmosphere. Soon there appears a noisy company headed by Rogozhin, who puts before Nastasya Filippovna eighteen thousand. For Gan’s sister and mother thing happening is intolerably insulting: Nastasia is a venal woman and should not be allowed in a decent house. She is the hope for enrichment for Gan. Scandal erupts: Gan’s perturbed sister Varvara Ardalionovna spits in his face, he's going to hit her, but Lev suddenly stands up for her. "Oh, how you will be ashamed of this deed!" this phrase tells everything of Myshkin’s incomparable gentleness. Nastasiay becomes enamored with him.
Conquered the beauty of Nastasiay, the prince visits her in the evening. Here bitty society is gathered. On the sudden question of Nastasiay, whether she should marry Gan, he responds negatively, and thus destroys Totskii’s plan. At half past eleven there appears the former company led by Rogozhin, who puts in front of Nastasiay one hundred thousand.
Again, in the center is Lev, he confesses his love to Nastasiay, and expresses his readiness to marry her. However, the decision was made Nastasiay rides away with Rogozhin and throws money into a burning fireplace, offering Gan to get them out of there. Gan, from last forces, makes himself not to rush after the outbreak of the money; he wants to leave but falls unconscious. Nastasiay herself grabs a pack and leaves the money for Gan, a reward for his sorrow.
Six months pass. During this time, according to rumors, Nastasiay almost ran from under the crown, preferring Lev to Rogozhin. Then she left him as well. At the train station, the prince feels someone's fiery glance. Prince visits Parphen in his dirty-green gloomy as a prison house on Gorokhovaya Street. Lev is haunted with visions of a garden knife lying on the table, he now and then takes it in his hands. Being exasperated, Rogozhin takes it away (Nastasiay will be killed with this knife). In Rogozhin’s house, Lev sees a copy of the painting by Hans Holbein on the wall, which depicts the Savior just taken down from the cross. Rogozhin says he likes looking at this picture. Lev cried out in amazement that "from this picture more faith may be lost," and Rogozhin suddenly confirmed it. The men exchanged crosses and they are now like brothers.
Approaching his hotel, Lev notices a familiar figure at the gate and rushes after her to the dark narrow staircase. Here he sees the same as on the station, sparkling Rogozhin’s eyes, he holds a knife. An attack of epilepsy happens to Lev.
Three days later after the attack, Lev moves to Lebedev's dacha, where there is also a family of Epanchins and, according to rumors, Nastasiay.The same evening he has a great society of acquaintances, who came to visit a sick prince. Later a group of young people led by a certain young man Burdovsky comes, allegedly Pavlishchev’s son. They are nihilists. Lampoon has read from a newspaper about the prince, and then they demanded that he as a noble and honest man should reward his benefactor's son. However, Gan Ivolgin, whom Lev ordered to do this business, proved that Burdovsky is not Pavlishchev’s son. The company retreats in embarrassment.
After another few days, Epanchins visit Lev and the grope goes for a walk. At the station, not far from them, there appears another company and Nastasiay. She familiarly refers to Radomski, reporting of the suicide of his uncle, who has squandered a large amount of the breechloader. Everyone is outraged by this provocation.
At the celebration of the birth of Prince Ippolit Terentyev reads what he has written "My necessary explanation", an amazing confession. After reading he makes a suicide attempt, but the gun has no cap. Lev defends Ippolit, who painfully afraid of appearing ridiculous.
In the morning on a date in the park Aglaia offers Lev to become her friend. He feels that he really loves her. Later in the same park, Lev meets Nastasiay, who stands in front of him on her knees and asks him if he is happy with Aglaia and then disappears with Rogozhin. It is known that she wrote letters to Aglaia to persuade her to marry Lev. Soon he is formally announced Aglaia’s fiancé. Aglaia appoints Nastasiay a meeting and comes along with Lev. Besides them, there is only Parphen. She strictly and unfriendly asks how Nastasiay dares to write her a letter and even to interfere in her personal life. Offended by the tone, Nastasiay urges Lev to stay with her and drives Parphen away. Lev immerses in the emotional turmoil.
The wedding of Lev and Nastasiay is planned. On the wedding day, on the way to the church, she suddenly rushes to Rogozhin in a crowd, who picks her up, sits down in the crew and goes with him away.
The next morning after her escape, Prince arrives at St. Petersburg and immediately rushes to his rival. He is not at home, but Lev fancied that he looks at him from behind the curtains. Lev goes to Nastasiay’s acquaintances, trying to find out something about her, several times returns to the Rogozhin’s house. Wandering continues all day. Finally, he meets Rogozhin, who asks to follow him. In the house, he leads the prince to the room where, in an alcove, on the bed under the white sheet, furnished with jars of fluid, so not to let the smell of putrefaction, lies dead Nastasiay.
The men spend a sleepless night over the body, and when the police open the door the next day, they find Parphen in delirium and Lev, who does not understand anything. The psyche of Myshkin is completely destroyed.