Francis Warren, Errol Flynn, appears to lead a respectable life as a financial investor, but he keeps a second, secret career as a writer of lurid detective novels under the pen name F.X. Pettijohn. His wife, Rita Warren, Brenda Marshall, remains unaware of this double existence, as does the rest of their social circle. Only Inspector Mason, Alan Hale, knows about the novelist’s persona, often mocking the idea that real crime is ever as straightforward as fiction.
Francis’s latest book ruffles feathers by quietly lampooning members of The Thursday Club, disguising real figures with thinly veiled aliases that include his wife and her mother, Agatha Archer, Lucile Watson. The revelation stings, and Rita and her mother decide to sue for libel. Privately, Francis counsels his lawyer, Wellington Carruthers, that such a suit would be good publicity for the book, urging him to lie to the women and delay action. Carruthers, who’s already known for a turbulent love life, is reminded that a happy marriage often hinges on not sharing every truth with one’s spouse. The conversation underscores Francis’s belief that a clever deception can maneuver a difficult situation, while Carruthers cautions against deceit.
Meanwhile, a man named Leopold Fissue attempts to blackmail Francis to help cash in uncut diamonds, threatening to reveal Warren’s secret life to the world. When Fissue is found dead aboard a yacht, the coroner and police attribute the death to heart failure caused by alcoholism. Francis, however, insists that Fissue was murdered for diamonds and refuses to disclose their prior contact. Inspector Mason and Detective Hoppy Hopkins challenge Francis to solve the supposed murder before the police do.
Clues surface in Fissue’s jacket—ticket stubs that point to Blondie White, a burlesque dancer played by Lee Patrick. Blondie becomes the prime suspect, and Francis reenters the scene in disguise as a man named “Tex” to woo Blondie and extract information. Blondie, though, has a solid alibi thanks to her dentist, Dr. Davis, Ralph Bellamy. Rita, watching Francis closely, spots him sneaking in late and concludes he’s having an affair, so she hires a private detective. The investigator soon trails Blondie’s movements and reveals the secret studio where Francis reportedly writes, hinting at liaisons that disturb Rita.
As Blondie’s performances and routines unfold, a new turn arrives when a call from the FBI links Fissue to a diamond-smuggling ring. Mason orders a second autopsy after a suspicious employer questions the cremation of the first corpse, but the coroner’s notes complicate the case. The police and Francis pursue Blondie, and a locksmith-like search for a missing suitcase in a locker emerges. The hunt narrows to Blondie’s apartment, where the investigators discover her dead body. A series of testimonies follows: a creditor spots a woman who left Blondie’s place without a heel on a Lake Drive road, and a taxi driver recalls dropping a woman off at that same location. Rita confesses that she also noticed a missing heel from her own shoe.
The tension tightens as Hoppy bursts into Blondie’s apartment with the taxi driver, uncovering the shocking truth: Francis is F.X. Pettijohn. Rita and her mother fear the social consequences of the scandal, while the police close in. Hoppy accuses both Francis and Rita of murdering Blondie and Fissue for the diamonds, but Francis resists arrest and tries to steer the investigation toward a different suspect. He theorizes that Dr. Davis supplied the poison used to kill Fissue, enabling Blondie to render Fissue drunk enough to mask the poison in an autopsy. Davis tries to silence Francis with a lethal confrontation, but Mason and Hoppy arrive in time to arrest him.
In a dramatic twist, Davis manages to slip away, only to learn on the radio that Francis supposedly fell from a roof while escaping custody. Believing himself safe, Davis returns to his office, where Mason and Hoppy wait to confront him—only to discover that the danger has not ended. With the threat lingering, Mason enlists Francis’s help for a new murder case, and Rita insists on accompanying him—much to her mother’s chagrin—setting the stage for a continuing collaboration between the writer and the detective, and a partnership that challenges their marriage and their loyalties alike.
