PlotSandra Carpenter (Lucille Ball) is an American who came to London to perform in a show but now is working as a taxi dancer. She is upset to find out that a friend, a dancer named Lucy Barnard (Tanis Chandler), is missing and believed to be the latest victim of the notorious "Poet Killer," who lures victims with ads in the newspaper's personal columns and sends poems to taunt the police.
Scotland Yard Inspector Harley Temple (Charles Coburn) asks if Sandra would be willing to work undercover to help find her missing friend and the killer. He sees first-hand how observant she is and gives her a temporary police identification card and a gun. Sandra is asked to answer personal ads, with a Yard officer named H.R. Barrett (George Zucco) always nearby, just in case.
By coincidence she meets the dashing man-about-town nightclub owner Robert Fleming (George Sanders), who at first wished to hire her for his stage revue but now wants to pursue a romance. In the meantime, Sandra answers an ad placed by Charles van Druten (Boris Karloff), a former fashion designer who is now mentally imbalanced. Her bodyguard Barrett has to come to her rescue.
She also needs to be saved, this time by Fleming, from a mysterious figure named Mr. Moryani (Joseph Calleia). He apparently recruits young women and whisks them off to South America by offering them a promising opportunity in a new land while, in reality, having something more sinister in mind.
Fleming shares a stately home with Julian Wilde (Sir Cedric Hardwicke), his business partner and best friend. Fleming ultimately does win Sandra's heart, even becoming engaged to her. Inspector Temple thanks her for her efforts and even agrees to come to their engagement party.
During the party at the beautiful home where she will soon live, however, Sandra accidentally discovers evidence that links Fleming to the Poet Killer's crimes, including a distinctive bracelet worn by her friend Lucy.
Fleming is placed under arrest. Circumstantial evidence mounts up, although he adamantly denies any involvement in the crime. Sandra believes him, but the Yard does not.
Lucy's body is found in the river. Wilde assures his incarcerated friend that he will hire the best possible attorney and do everything possible to clear him. It occurs to Inspector Temple that it is actually Wilde who fancies poetry and is in a position to have been the killer.
Just before he can flee, Wilde is visited by Sandra at home. He is secretly obsessed with her, just as he possibly was with the other women he abducted. Wilde at first expresses his desire for Sandra, then removes his scarf and prepares to strangle her. Scotland Yard's men break through the windows to rescue her just in time.
Fleming is set free, and he and Sandra toast with champagne to better days ahead.
- George Sanders as Robert Fleming
- Lucille Ball as Sandra Carpenter
- Charles Coburn as Inspector Harley Temple
- Boris Karloff as Charles van Druten
- Sir Cedric Hardwicke as Julian Wilde
- Joseph Calleia as Dr. Nicholas Moryani
- Alan Mowbray as Lyle Maxwell alias Maxim Duval
- George Zucco as Officer H. R. Barrett
- Robert Coote as Detective
- Alan Napier as Inspector Gordon
- Tanis Chandler as Lucy Barnard