A young doctor in Los Angeles named John Wesford becomes a suspect when a series of Jack the Ripper copycat killings is committed. He and another young doctor (Jack Pendler) are at the scene of the final crime in the series; they know each other because they both work for the same medical unit, reporting to the abusive Dr. Sidney Tannerson. Pendler seems to realize that John Wesford's testimony will likely lead to his being arrested as the killer, and in an ambiguously staged scene, murders him, staging the scene to resemble a suicide. The police quickly name John Wesford as the copycat killer and hypothesize that he killed himself out of guilt.To the surprise of everybody involved, John Wesford's identical twin brother, Rick, arrives and claims to know his brother did not kill himself because he has seen visions of the true killer. In flashbacks, the viewer sees that Rick Wesford saw Jack Pendler killing his brother. The police humor Rick briefly, but only because his existence calls into question the eyewitness testimony that had put the identical-looking John at the scene of the crime, and Rick's suspicious knowledge of the crime scene (from his visions) make him an attractive suspect himself. Under scrutiny by the police, Rick allies himself with another of his brother's colleagues, Dr. Chris Moscari, and carries out his own investigation. He successfully identifies, tracks down, and confronts Pendler, who attacks him and is arrested. Pendler is in some regards an excellent suspect - physical evidence puts him at the scene of the final murder. But in other regards he is a terrible one, not matching known characteristics or habits of the killer.Rick continues to dream about his brother's murder and asks the police psychologist to hypnotize him to clarify these visions. In the refined vision he again sees Pendler attack his brother, but also notices that Pendler's shoes do not match those worn by the copycat killer, and that Dr. Tannerson had been at the scene. He intuits that Tannerson will next attack Dr. Moscari and speeds to her house, attracting a string of police cars with his reckless driving. Moscari survives and Rick avenges his brother's death by killing Tannerson, who (it is implied) had manipulated Pendler into murdering the unfortunate twin.