The narrative begins with a young romantic poet, Octavius, hopelessly in love with Ann Whitefield, unaware that her late father has appointed the radical thinker John Tanner as her joint guardian alongside the conventional Roebuck Ramsden. Tanner, who has written a revolutionary handbook on the futility of traditional morality, dreads Ann's calculated charm and considers her a relentless predator bent on capturing him. Meanwhile, the respectable society of the characters is thrown into turmoil by the apparent scandal of Violet Robinson's secret pregnancy, which turns out to be a legitimate marriage she has concealed. Tanner flees to the Sierra Nevada in an effort to escape Ann's matrimonial designs, but his motor car breaks down, leading to an encounter with a band of philosophical brigands led by Mendoza, a former waiter desperately in love with a woman named Louisa.
During his captivity, Tanner experiences a surreal dream sequence in hell, where Don Juan, the Statue, the Devil, and Dona Ana debate the eternal conflict between human illusion and the relentless evolutionary drive of the Life Force. Awakening from this philosophical vision, Tanner finds that Ann has tracked him across Europe with the determination of a hunter, accompanied by an American suitor and the rest of the bewildered party. As the reality of the pursuit closes in, Tanner realizes that resistance is futile against the biological imperative of the race, leading him toward a reluctant surrender to marriage.
