Maurice is a moderately successful writer living on the south side of the Common in London. Driven by a cynical outlook and dogmatic atheism, he originally pursued a relationship with Sarah Miles to research a novel about civil servants. He harbors intense feelings of jealousy and bitterness toward both Sarah and her husband Henry following the abrupt end of his affair with Sarah eighteen months ago. He writes methodically, completing exactly 500 words each day regardless of his emotional state.

Sarah is Henry's wife and Maurice's former lover. She maintains a polite, quiet domestic routine with her husband while keeping her deeper emotional conflicts completely concealed. Though she broke off her affair with Maurice eighteen months ago, she continues to occupy his thoughts entirely. She suffers from a persistent, lingering cough and privately records her philosophical struggles in a hidden diary.

Henry is a mild-mannered, routine-driven civil servant and Sarah's husband. He views Maurice as a trusted friend, completely unaware of the past affair between Maurice and his wife. He worries about Sarah's recent detached behavior and long walks, but he lacks the confrontational nature to address his suspicions directly, preferring instead to ask Maurice for advice.

Mr. Savage is a professional private detective who operates an agency in London. He maintains a polite, clinical demeanor, treating his clients' jealousies and suspicions with the detached efficiency of a medical professional diagnosing a symptom.

Parkis is an investigator working for Mr. Savage's detective agency. He carries out the groundwork of tailing Sarah, collecting documents, and reporting back to Maurice. Earnest but sometimes clumsy, he frequently brings his young son along on his surveillance assignments.

Lance is Parkis's young son. He assists his father during investigative assignments, occasionally acting as a prop or an excuse to gain access to private locations, such as when Maurice pretends the boy is ill to enter a stranger's house.

Richard is an evangelist for rationalism and atheism who lives on Cedar Road. He delivers public lectures on the Common attacking religious belief. He has a prominent birthmark on one side of his face, which makes him self-conscious but does not deter his fierce philosophical debates.

Miss Smythe is Richard's middle-aged sister. She lives with him in their Cedar Road flat and helps maintain their extensive rationalist library, welcoming guests who show interest in their secular ideology.

Father Crompton is a strict Catholic priest in London. He holds firm views on religious doctrine and frequently finds himself at odds with the atheistic Maurice during heated conversations about faith and the nature of belief.

Mrs. Bertram is Sarah's elderly mother. She harbors a complicated personal history with Catholicism and views her daughter's life choices through the lens of her own past decisions regarding baptism and faith.

Waterbury is a literary journalist writing an article about Maurice Bendrix's career. He is somewhat irritable, highly protective of his professional standing, and easily annoyed by interruptions during his interviews.

Sylvia is a young, attractive woman working as an apprentice to Waterbury. She is observant and willing to assist Maurice with directions when her employer proves uncooperative and cuts their meeting short.