One night, on a bank of the river Seine near Clichy, two tramps, Mouton and Bébé Rose, are awakened by a series of disturbing noises: car doors slamming and a big splash. The two men soon catch sight of a body floating on the water. Undeterred by danger, Mouton dives in the river and, with the help of his friend, manages to pull out a young lady, who happens to be still alive. But although a hero, people only see Mouton as a bum and he does not get the credit he thinks he is entitled to. He therefore decides to go further and to lead his own investigation...
