The novel takes place in a prison and relates the final twenty days of Cincinnatus C., a citizen of a fictitious country, who is imprisoned and sentenced to death for "gnostical turpitude." Unable to blend in and become part of the world around him, Cincinnatus is described as having a "certain peculiarity" that makes him "impervious to the rays of others, and therefore produced when off his guard a bizarre impression, as of a lone dark obstacle in this world of souls transparent to one another." Although he tries to hide his condition and "feign translucence," people are uncomfortable with his existence, and feel there is something wrong with him. In this way, Cincinnatus fails to become part of his society.
While confined, Cincinnatus is not told when his execution will occur. This troubles him, as he wants to express himself through writing "in defiance of all the world's muteness," but feels unable to do so without knowledge of how long he has to complete this task. Indifferent to the absurdity and vulgarity around him, Cincinnatus strives to find his true self in his writing, where he creates an ideal world. Taken to be executed, he refuses to believe in either death or his executioners, and as the axe falls the false existence dissolves around him as he joins the spirits of his fellow visionaries in "reality."
Other characters include Rodion the jailer, the director of the jail Rodrig, and Cincinnatus' lawyer Roman. Some suggest that these names are meant to mimic that of the protagonist of Fyodor Dostoyevsky's Crime and Punishment , Rodion Romanovich Raskolnikov. Cincinnatus' wife Marthe, a child named Emmie, and fellow prisoner "M'sieur Pierre"(subsequently revealed to be the executioner) are also secondary characters.