One Christmas Eve in Paris, Robert Herbin picks up an attractive young woman, Martha Dravet. After leaving her daughter at their apartment on the upper floor of her husband's book warehouse, Martha goes with Robert to his lodgings. On returning to her home later, they find her husband dead, an obvious suicide. Robert, an ex-convict who is breaking parole by being in Paris, persuades her not to call the police. He leaves, but his curiosity makes him linger long enough to see Martha and her child leave and head toward a church. She faints at mass, and a tipsy automobile salesman named Adolphe Ferry takes her back to her apartment. Robert is amazed that the body has disappeared, and he watches the two leave. He waits until they return, hours later, but this time the body is again in the apartment. Adolphe telephones the police and leaves after they come and take the body away. Robert confronts Martha, and she shows him two identical rooms on separate floors and admits that she had fatally drugged her husband and faked his suicide; she needed a stranger, Robert, in order to establish an alibi. They burn all the furnishings of the upstairs apartment, but Martha accidentally places the wallet left by Adolphe in Robert's coat. Later, when the police arrive at the ex-convict's apartment to question his presence in Paris, he unwittingly hands them the wrong wallet. Upon seeing Adolphe's papers, they urge Robert to reveal his part in the death, but Martha arrives and confesses everything.
