Bourgeois Parisian bookseller Edouard Lestingois (Charles Granval) rescues a tramp, Boudu, from a suicidal plunge into the river Seine. Boudu is brought into Lestingois' household and invokes the age-old principle that the book-seller is now responsible for his life. The family adopts the bum and dedicates itself to reforming him into a proper middle class person. Boudu (Michel Simon) shows his gratitude by shaking the household to its foundations, challenging the hidebound principles of his hosts and seducing them with his anarchic charm.