Actor Richard Sand is appearing on the London stage in a new production based on the career of Jack the Ripper. When a series of actual murders are committed in a manner similar to those depicted in the play, police suspicion falls on all those connected with the production, Richard in particular. At the same time Richard is deeply troubled by his love for Ann Morlay, a Parliament member's daughter who is already engaged to one of Richard's best friends, Dr. Morley Greely. Despite intensive questioning by the police, Richard continues in his role, until, during a performance, he discovers that a real knife has been substituted for a stage prop. After rushing from the theater, he is led by a mysterious telephone message to the room of a prostitute who has just been slain. The police arrive and are about to arrest him when a little girl announces that she saw the real killer. Richard cooperates with Scotland Yard in setting a trap for the modern-day Jack the Ripper, who turns out to be Greely. Jealous of Richard's love for Ann, Greely had tried to frame his friend for the brutal murders. With Richard cleared of suspicion, Greely commits suicide before the police can close in on him.