A criminal psychologist investigates the murder of a veteran with amnesia.

At his office, detective psychiatrist Dr. Robert Ordway meets with a war veteran who is suffering from bomb shock and combat fatigue, and who has an inexplicable fascination with a particularly tough neighborhood in the city. Later that evening, when Ordway visits the neighborhood to search for clues to his patient's behavior, he happens upon a murder scene, and immediately realizes that his patient is the victim. When two men escape with the dead body, Ordway summons police inspector Harry B. Manning to the scene. Manning begins an investigation into the murder by questioning the landlady of the building from which the two men were seen fleeing. The police also search other rooms in the apartment building, but they find no clues. Recalling his brief meeting with the murder victim, Ordwawy remembers that his patient had mentioned an astrologer named Alfredi, who predicted that he would meet a violent death. While Ordway tries to find Alfredi, the two men seen carrying the dead body out of the apartment building pay a visit to a mysterious blonde woman. The woman, who hired the two men to dispose of the body, refuses their demand for more money and sends them away. As the police investigation continues without the discovery of a single clue, Manning begins to doubt Ordway's assertion that a murder actually took place. Ordway, however, is determined to find the killer, and continues his investigation by acquainting himself with Ruby Farrell, who lives in the apartment building where the man was murdered and who runs a shooting gallery concession at a carnival. Ruby takes Ordway to an abandoned house next to her apartment building, and when Ordway enters the house alone, he is knocked unconscious by the two men working for the blonde woman. The next day, the police find the dead body and the victim is identified as Philip Armstrong. When it is determined that Armstrong was killed by a type of air pistol used at carnivals, Manning arrests Ruby on suspicion of murder. Ordway, however, does not believe that Ruby is the killer, and decides to track down the owner of the abandoned house, Gerald Cotter, who happens to be the father of Philip's fiancée Irene. Gerald insists that the house has been abandoned for years, and provides Ordway with no further clues. A short time later, when the killer's two accomplices are discovered murdered in an apartment, Ordway finds an address book at the scene containing Alfredi's address. Alfredi is then brought to the police for questioning, and he confesses that a woman named Natalie hired him to put a scare in her sister's fiancé. Natalie, it is soon learned, is Irene's estranged sister, and died six weeks earlier, so she could not have been involved in any of the murders. Hoping to catch the killer in action, Ordway sets a trap at the abandoned house. His plan succeeds when Irene, disguised in a blonde wig that makes her resemble her dead sister, emerges from a darkened corner with her gun drawn. When Manning bursts into the room, Ordway disarms Irene and exposes her as the killer. Ordway then pieces together the mystery and explains to Manning that Irene suffers from a mental condition stemming from the death of her sister, and that she so strongly relied upon her sister's strength that she occasionally assumed her identity. He also explains that Irene decided to kill Philip when Philip discovered her split personality.