Michel is 27 years old when he invites three close friends to his North African home to recount the past three years of his life. At age 24 he is a bookish historian who weds Marceline in an arranged marriage. He does not love her initially, but her efforts nursing him back to health after he catches tuberculosis makes him fall in love with her deeply. Michel's mental transformation throughout The Immoralist strains his relationship with Marceline. While recovering his health, he casts off society's beliefs about respectability. He wants only to attain sensual pleasure and live a life of the body rather than of the mind. Michel's transformation causes his downfall. By the end of the novel, Marceline is dead and Michel has spent most of the great fortune he and his father made before the novel begins.
When Marceline marries Michel, she is a devout Catholic. Although Michel does not believe in God, she loves him dearly and tends to his every need as he recovers from tuberculosis in Biskra, a city in French Algeria. Her efforts to help sick Arab children reveal that she gains great pleasure from helping the weak and needy. Marceline's pregnancy and miscarriage bring great strain to her and Michel's relationship. She contracts his tuberculosis and her health declines throughout the story. Michel's changing personality affects her mentally. Just before her death, she refuses to grasp the rosary that gave her comfort in years past. After Marceline dies Michel buries her in a French Algerian garden she loved visiting when Michel was recovering.