A series of crimes is being perpetrated around a famous singer. Strangely, during each of the crimes, the artist's voice is heard humming his favorite song. Suspicions lead to a chase through a nocturnal Paris, ending in a disused theater where the assassin has lured his final victim.
Somewhat reminiscent of 'Mädchen in Uniform' (1931), the story is set in a private girl's school, populated almost exclusively by children from broken homes. Among the few students who can claim family stability is Micheline Presle, but even her happiness is threatened when her lawyer father Andre Luguet inaugurates an affair with stage actress Jacqueline Debulac. With the help of Debulac's daughter Louisa Carletti, Presle is able to break up her father's romance and deliver him into the open arms of her mother Marcelle Chantal.