Arriving in New York City for a Christmas visit with her aunt, Nicki Collins sees through her train window the murder of shipping magnate Joseah Waring. Because of her known addiction to mystery novels, the debutante is unable to convince the police that she witnessed a crime, and decides to begin her own investigation. After viewing a newsreel in which Waring is reported to have died accidentally while decorating a Christmas tree at his Long Island estate, Nicki sneaks onto the property, only to be discovered by Arnold Waring, Joseah's nephew. Arnold, however, mistakes Nicki for Margo Martin, a nightclub singer and Joseah's fiancée. Posing as Margo, Nicki is then allowed to witness the reading of Joseah's will, in which the tycoon disinherits his family and leaves the bulk of his estate to Margo. Later, while searching Joseah's room, Nicki finds the bloody slippers the tycoon was wearing when he was killed, but Mr. Saunders, Waring's personal secretary, sends Danny, a chauffeur, to Nicki's hotel room to recover the incriminating evidence. Nicki then goes to The Circus Club to see Margo, but when Arnold shows up, Nicki is forced to lock the singer in her dressing room and perform in her place. Nicki is later waylaid by Saunders and Danny, but she is soon rescued by mystery writer Wayne Morgan, at the cost of his engagement to long-time fiancée, Joyce Williams. Saunders is then killed, allowing Nicki and Wayne to sneak out of the nightclub with the slippers. The two are arrested the next morning for the nightclub murder, and evidence of their innocence is destroyed when Maxwell, Wayne's valet, cleans Joseah's bloody slippers. Nicki is later bailed out of jail by Arnold, but she runs away as she suspects him of the murders. She then mistakenly seeks the protection of Jonathan Waring, Arnold's older brother, unaware that he is the psychopathic killer. Nicki suddenly realizes the truth when she discovers that she is in the same room in which Joseah was killed. Jonathan tells Nicki that he plans to kill her, then frame his brother for the murder. Arnold manages to rescue Nicki, only to have Wayne arrive, mistake him for the killer and give Jonathan back his gun. Wayne is followed to the Waring warehouse by the police, however, and Jonathan is finally arrested. Later, Nicki and Wayne marry, and the writer is forced to tell his new bride the ending of his latest book in order to begin their honeymoon.