Irma is one of Paris' most successful poules (tarts). She falls in love with Nestor, a penniless law student. She decides for the first time in her life she will have a mec (pimp). Nestor is jealous of Irma's customers and decides he must become her only buyer, so he disguises himself as Monsieur Oscar, a rich old fossil who asks only for companionship, yet provides enough grisbi (money) to become her exclusive patron.
Nestor soon becomes exhausted from his numerous jobs, studies, and lovemaking. Irma decides that Oscar is not getting his money's worth and seduces him more passionately that she ever has Nestor. This makes him more jealous than ever and he decides that Oscar must die. However, in killing-off his alias, Nestor is convicted of murder and sentenced to Devil's Island. When he learns Irma is with child he escapes on a raft and finally proves (by paying off the judge) that he and Oscar are one and the same -- all this in time to witness the birth of his child on Christmas Eve.