Dorval, a wealthy stock broker, is found murdered in his library by his wife, who has just returned from an out-of-town visit. Detective Humbert finds on his desk the card of one Duruy, who owed Dorval a considerable sum of money. He trails Duruy, who proves an alibi, which satisfies the police, but does not convince Humbert. In his close association with Dorval’s widow, Humbert falls madly in love with her, and she, thinking only of revenging her husband’s violent death, unconsciously encourages him, Duruy meets Humbert and Dorval’s widow at a mask ball and is attracted to Mme. Dorval without knowing who she is. Another man is arrested tor Dorval’s murder. At his trial evidence is introduced to show that the accused man had struck Dorval for speaking to his sweetheart and had left him for dead, but Dorval did not die at this man’s hands. He was murdered in his library, killed by a knife thrust. Duruy is seized with an attack of epilepsy and confesses the crime. Pursued by Humbert, he jumps into the lake and is drowned. Thus does justice triumph beyond the pale of the law.