Larry Morgan (Kent Taylor), a private detective, is hired by a woman who wants Larry to trail her husband. The husband is murdered and, shortly afterwards, the wife is also killed. Larry shuffles through a long list of suspects before revealing the killer...

At the Personal Research Council detective agency, president and treasurer Larry D. Morgan and his secretary, Daisy "Dizzy" F. Nelson, are in desperate need of new clients. One day, a woman named Mrs. Swann visits the office and asks Morgan to investigate her physician husband Kenneth, who she feels has been concealing something from her. However, a short time later, Dr. Swann is found murdered at the studio of painter Peter Vandaman, one his clients. When Morgan tries to return Mrs. Swann's money, she tells him to keep it and find her husband's murderer. Mrs. Swann later tells Morgan that the only thing missing from her husband's body was a set of keys. At the site of the murder, Morgan questions Vandaman, but he provides Morgan with a believable alibi. Morgan then goes to Dr. Swann's office, where he discovers Miss Phillips, Swann's receptionist, looking through the doctor's files. Phillips admits that she was in love with her boss, but provides him with no further clues. After tracing the last phone number that Dr. Swann dialed to actress Paris Wood, Morgan, posing as a newspaperman, drops by her dressing room. There he is introduced to Jeffrey Regan, Wood's producer and fiancé. Morgan startles Wood with questions about her telephone conversation with Dr. Swann, and is soon asked to leave. Miss Phillips later visits Morgan and recalls that she had seen her boss pick up a key that looked like it belonged to a public locker. After determining that Mrs. Swann has the key, Morgan goes to her home to look at it, but is clubbed on the head by Vandaman, who came to discuss Swann's death and does not want to be incriminated. When he regains consciousness, Morgan discovers that Mrs. Swann has been killed. Morgan surprises Vandaman at his studio and demands to know why he killed Mrs. Swann, but Vandaman insists she was dead when he arrived. Vandaman then tells Morgan that he recalls overhearing a quarrel between Dr. Swann and Steven Loring, who accused Dr. Swann of having an affair with his wife. Morgan visits Loring's alcoholic wife and, while questioning her, learns that she met a man named Swann at the Key Club. Morgan and Dizzy go to the Key Club, where they witness the jealous Loring assault Regan. Morgan is then forced into a car by two gangsters, who try to get him to divulge the location of "the key" by beating him. Morgan escapes, however, by jumping through a window, then hitches a ride from a woman named Heidi, who was at the club. Heidi takes Morgan to her home and tries to slip a narcotic into his drink, but he switches the glasses and watches as she loses consciousness. Seeing the name of psychic Huntley G. Harlow on Heidi's car keys, Morgan pays Harlow a visit, posing as a new patient. No sooner does Morgan tell Harlow some of the details of his investigation, than the psychic reveals his complicity in the crime by asking to purchase the key from him. Loring later reveals to Morgan that his wife was first married to Regan's uncle, who died and left her a great sum of money. Morgan and Loring's conversation is interrupted by the police, who tell them that Harlow has been found murdered in the Loring home. As Morgan questions Mrs. Loring about her first husband's death, Loring tricks his wife into confessing that she murdered Harlow and Swann, and that she conspired with Swann to kill her first husband. Swann later blackmailed her and the evidence, in the form of a statement by Swann, was in the locker. The key to the locker, which Morgan had previously visited, is found in Mrs. Loring's house, definitively linking her to the murders, and her arrest closes the case for him.