Overcome with grief after losing his dog, a homeless man named Boudu (Michel Simon) throws himself into the Seine. But his suicide is interrupted when Edouard Lestingois (Charles Granval), a compassionate book dealer, spies him drowning and saves his life. Taking Boudu into his bourgeois home, Edouard hopes to give him a makeover. But the vagabond's unexpected effect on Edouard's family makes the Samaritan reconsider his good deed.