Joe Powell, a publicity director for a film studio, visits his girlfriend Susan Cooper after a day at the studio. Their quiet evening is shattered by a scream from the hall: Ellen Smith, who lives across the way, has been strangled in her apartment. As the case unfolds, the headlines shift when an actress, Mona Harrison, who recently vanished, suddenly dominates the news. The police chief, Chief Williams, questions everyone who attended Mona’s dinner party the night before and learns that Mona’s servants quit after she suggested they all go out to dinner but never showed up at the restaurant.
In a tense late-night turn, Susan searches Mona’s bedroom, discovers a safe, and hides in a closet when a man enters. She is almost strangled before a dramatic interruption by Detective Hoffman, and the intruder escapes. The investigation deepens: Ellen was murdered by a man, while Mona’s death is attributed to a woman, steering the mystery toward dual motives and hidden lives. As Joe delves into Mona’s records, he becomes wary of the danger and is nearly killed by an unseen assailant while he checks Mona’s files for clues about her twin sister, Marie.
With Mona’s safety a growing concern, Susan decides to head for Reno, Nevada. Fearful for her, Joe partners with Hamilton Hart and Carol Lynn as they chase Mona’s trail westward. Along the way, Susan is almost driven off the road by Arthur Evans. Upon arriving at the Reno hotel, Susan, Joe, Hart, and Carol finally cross paths with Mona’s sister, Marie, who has been implicated in the web of blackmail surrounding Mona. Susan reveals that Arthur was married to Marie and that the two of them have been coercing Mona into paying for their silence. The investigation leads to a violent confrontation: Mona is killed by Marie after refusing to pay more, and Arthur kills Ellen, who had witnessed Mona’s murder. In the furious sequence that follows, Marie erupts with violence and ultimately falls to her death from the hotel window, leaving the case resolved but shrouded in tragedy.
