Nabokov's Invitation to a Beheading tells the story of the enigmatic Cincinnatus C., a thirty-year-old prisoner and former teacher who has been sentenced to death for the crime of "gnostical turpitude". He is to die in twenty days time, although he is never made aware of this deadline, and the novel follows his remaining days of life.

The jailer, Rodion, takes Cincinnatus to the "fortress", where Cincinnatus converses with his lawyer and then shares a dance with Rodion. Afterward, he writes down his thoughts, and we learn that Cincinnatus does not know the date of his execution and wishes to so that he knows whether or not he has enough time to write about his experiences. He asks several characters to tell him when it is, but he is unable to learn. At some point, he is assigned a cellmate by the prison director, Rodrig. After meeting Rodrig's daughter, Emmie, Cincinnatus is taken into the hall by Rodrig to observe this cellmate through a peephole.

We learn that Cincinnatus has a wife, Marthe, whom he loves but who is not loyal to him. He eagerly expects her to visit him in prison, but she postpones her visit. When Cincinnatus is allowed out of his cell in order to clean it, he wanders the vicinity, dreaming of escape. He sees Emmie playing in front of a picture of a garden, which he mistakes for a window. The following morning, Cincinnatus meets his cellmate at last: Monsieur Pierre. Cincinnatus dislikes him, but the prison director behaves otherwise.

After a little over a week in prison, Cincinnatus starts writing again, confessing his fears and angst about how society perceived him even when he was a free man. He finally gets a visit from Marthe, but she arrives with her lover. Cincinnatus is unable to meet with her because his cell is cluttered with furniture in preparation for the visit. He gets another visit, this time from his estranged mother, Cecilia. Cecilia tells him about the strange circumstances surrounding his birth and the identity of his father. That same night, Pierre digs a tunnel through their cells and invites Cincinnatus into his. Cincinnatus instead emerges out of another hole, where Emmie is waiting to take him to a dining room. There, Cincinnatus finds Rodrig and his wife dining with Pierre. They ask Cincinnatus to join them, and then Rodrig shows Cincinnatus a photo album detailing Emmie's future.

At last, Rodrig is revealed to be Cincinnatus' executioner, and Cincinnatus is finally told the date on which he is to die: "the day after tomorrow". Cincinnatus once again writes about his fear. Marthe visits him one more time, asking Cincinnatus to repent for his crimes. Cincinnatus finally dismisses her. The day of his execution arrives, and Cincinnatus is taken to the town square in a carriage. A crowd has already formed, and he climbs up the scaffold. He counts backward from ten in preparation for the beheading. Suddenly, he gets up, and steps off the scaffold; implying that his soul has left his body for good.