Antoine is a 30-year-old, reclusive historian living completely alone in the fictional French city of Bouville. He supports himself on savings while researching an 18th-century aristocrat in the local library. Profoundly alienated, he observes the world with intense, clinical detachment. His daily encounters with mundane objects trigger a growing existential crisis that makes him physically ill.

Ogier P., known to Antoine as the Self-Taught Man, is a clerk who dedicates all his free time to rigorously educating himself at the public library. He is an avowed humanist and socialist who believes in the inherent worth of all humanity. His optimistic love for people directly contrasts with Antoine's cynical isolation.

Anny is Antoine's ex-lover, a theatrical and once-carefree Englishwoman who used to travel the world with him. In the past, she actively curated her life to create "perfect moments" with profound emotional resonance. She serves as a vital link to Antoine's history and represents his ongoing struggle to reconcile memory with the present.

Françoise runs the Railwaymen's Rendezvous, a café located near the Bouville train station. She maintains a completely mechanical, detached sexual relationship with Antoine. Her presence offers Antoine a brief, habitual reprieve from his overwhelming loneliness, though they rarely speak during their encounters.

The Marquis de Rollebon is a fictional 18th-century French aristocrat whose letters and treatises are the sole focus of Antoine's days in Bouville. Though long dead, Rollebon functions as a living presence in Antoine's mind, representing his attempt to find structure and purpose through historical research.

Monsieur Achille is an eccentric local man whose odd behavior alienates him from normative society. Antoine recognizes a kinship with Achille, suspecting the man suffers from a similar sense of anxiety and disconnection from the world.

Doctor Rogé is a conventionally successful and well-adjusted professional in Bouville. He uses his societal authority and medical background to confidently diagnose others, categorizing eccentricities in a way that enforces social norms and soothes public anxiety.

M. Fasquelle is the owner of the Café Mably, an establishment Antoine frequents. His temporary absence due to illness severely disrupts Antoine's sense of routine, triggering intense anxiety about the fragility of human existence and the illusion of stability.