Los Angeles police detectives Lt. Andy Doyle and Sgt. Mike Duncan are assigned to investigate the murder of Fred Horner, who has been strangled at the Sunset Villa Motel in West Hollywood. Horner's body was found in the unit occupied by his neighbor, Henry Johnson, who is now missing. Dick Harris, the motel's owner and manager, is convinced that Henry committed the murder as he had heard the two men arguing. Henry, a gambling addict, explains to his fiancée, Mary Raiken, that during a card game, he went into the kitchen to make some drinks and asked Horner to go to his unit for ice. When Henry emerged from the kitchen, he found Horner dead on the floor, panicked and ran away.
After Henry refuses to turn himself in to the police, Mary manages to convince him to go to see his psychiatrist, Dr. Green, who has been treating him for his compulsive gambling problem. Meanwhile, in an attempt to elicit information about Horner, Mike talks with Pat Orvello, the assistant manager at a gas station where Horner had his car serviced. When Dr. Green advises Henry to turn himself in, Henry leaves and attempts to buy a bus ticket for San Francisco, but is spotted by a deputy who sees him escape in a taxi. In the course of his investigation, Mike discovers that the frugal Horner had one hundred thousand dollars in his bank account and that Henry had just cashed two five-hundred dollar checks from Horner. After a plainclothes deputy, who has been tailing Mary, advises Andy that she is waiting for someone in a drug store coffee shop, Andy and Mike go there and when Henry arrives, arrest him. In jail, Henry explains how he became involved with Horner: Although Henry told Horner that he had a very serious gambling problem and was trying to quit, the older man lured him into a game of poker.
They played frequently and Horner became increasingly angry as he kept losing and insisted upon trying to win his money back. On the night of the murder, Horner left to get some ice from his room and soon after, Henry found him dead. After Henry insists that he did not kill Horner and had fled only because he feared that he would be incriminated, Andy, believing that Henry may be innocent, returns to the Sunset Villa Motel, then visits the adjacent Sunset Vista Motel. Andy suggests to Mike that perhaps the murderer had confused the motels, which have identical bungalows, and was actually after a Mr. Bradbury, the occupant of room eight, Horner's room number in the other motel.
Mike investigates Bradbury and learns that he runs a chemical laboratory that prepares vaccines against animal diseases and is in town for only a few more days. Andy talks with the gregarious Bradbury, and upon discovering that he carries a large amount of cash, three thousand dollars, with him, convinces Bradbury to become bait for the killer by flashing his wad of bills at different establishments he has been patronizing. Andy also persuades his chief to free Henry, who reconciles with Mary and agrees to start a new life with her. Bradbury goes to Orvello's gas station to leave his car for overnight servicing and flashes his money roll. That night, Andy, Mike and two officers stake out both motels and observe a shadowy figure enter Bradbury's room through a window. Bradbury is about to be strangled when Andy rushes in, but the assailant escapes into the communal parking lot and becomes involved in a shootout with the officers.
When Henry drives up with Mary to retrieve some items from his room, the killer slugs him, pushes Mary out of the vehicle and drives off, but is soon captured. Later, Andy and Mike explain to Henry and Mary that the killer was Orvello, on the run for crimes committed on the East Coast, who had seen Bradford's money roll, but had gone to the wrong motel. After killing Horner by mistake, Orvello, who had heard the men arguing, dumped the body in Henry's room to incriminate him. Henry and Mary thank Andy and Mike, then head to the marriage license bureau.
