The novel is a picaresque adventure tale that follows the life of Felix Krull, a German man, who, after his father’s champagne business fails, moves to Paris and begins a double life. With the name Armand, he works in a hotel and becomes a jewel thief as well as the lover of the wealthy, masochistic Madame Houpflé; at night, Felix enjoys Parisian society. His involvement with the Marquis de Venosta leads to impersonating him while traveling so that the young aristocrat can stay in Paris with his mistress. In Portugal, the disguised Felix takes advantage of an introduction from Professor Kuckuck and, in his absence, seduces the learned man’s wife and daughter.

Felix is presented as having a lifelong fascination with masks and artifice, and as a young boy, he contemplates becoming an actor. Realizing that real-life pretense is more lucrative and entertaining, he applies his talent for impersonation wherever and whenever it most suits him. A kind of modern-day Casanova with something of Candide’s innocence, he navigates society largely through his sexual charm. That Felix succeeds in his amorous conquests, goes unpunished for his illegal activities, and does not receive his comeuppance is consistent with Thomas Mann’s adaptation of the picaresque genre. And just when it seems that learning about human nature from the scientist Kuckuck (whose name strongly suggests "cuckold") might spark his rehabilitation, instead, Felix abuses their relationship by making love to the women in his family. Although it would be a stretch to paint Felix as an existential anti-hero, from Mann’s celebration of his escape from justice, the reader can infer the author’s critical view of the society that produced such an amoral man.