Priape Boudu (Michel Simon), a Parisian street tramp, decides to end his destitute life by plunging into the Seine. Hidebound middle-class bookshop owner Edouard Lestingois (Charles Granval) saves the tramp's life and brings him home for dinner. Touched by his story, Edouard and his wife, Emma (Marcelle Hainia), allow Boudu to live in their house so they can reform him into a model bourgeois citizen, but unexpected events unravel their well-intentioned plans.