The musical tells the story of a poor law student, Nestor le Fripé, who falls in love with a wealthy prostitute, Irma la Douce. He becomes insanely jealous of her clients and decides he cannot stand her being with another man. He decides that he must become her only buyer and disguises himself as Monsieur Oscar, a wealthy old man who visits and pays Irma for only companionship. In order to pay Irma enough to be her exclusive patron, Nestor (Oscar) works numerous jobs along with going to school. He soon becomes exhausted living out his plan and decides that he must destroy his alter ego. When ‘Oscar’ disappears, Nestor is convicted of murder. By briefly assuming his disguise once more, he manages to prove his innocence and all ends well.