London is terrorized by a mass-murder, "The Avenger," who preys on blonde women.

Soon after the latest murder, a mysterious man (Ivor Novello) comes to lodge in the house of a family who has a pretty, blonde daughter. His unusual habits disturb her parents but she finds herself strangely attracted to him.

Her jealous boyfriend, a police detective, is bent on keeping them apart and tries to have him arrested when he believes this lodger is actually the serial killer.

Hitchcock wanted an ambiguous ending but the studio wouldn't allow it implied that Novello might actually be the murderer.

Third Hitch film, but first to be released. First Hitch cameo (in the pressroom).

Novello, a big star in his day, was alleged to be the "Rock Hudson" of his generation. Take note of some of the title cards which allude to his "secret."

Glass ceiling was constructed to see Novello's pacing overhead.