Author of the best-selling crime novel Le Poulet se mange froid (Chicken Eats Cold) under the pseudonym Sam O'Connor, Inspector Bourdieux's daughter, Agnès, is unwillingly drawn into the gangster ring by two small-minded young misfits, Dédé and Juju. She's not insensitive to the charms of M. Paul, a false kingpin who is in fact a son of a good family and a thrill-seeker. Planning a heist at the home of one of Paul's snobbish friends, she arrests the real Sam O'Connor, an escaped convict, with the help of her father. Then she and Paul confess their love for each other.