In San Francisco, the corspe of Jefferson Monk, which was beheaded in an automobile accident, is delivered to the morgue. Meanwhile, at the Silver Samovar Club, acclaimed detectives Jack Packard and Doc Long recall how they learned about the prophesy of Monk's death: Three days prior, the detectives meet Monk at a nightclub as he is menaced by an argumentative woman and a flaming dessert. After the dessert explodes and nearly chars Monk, the detectives extinguish the flames and Monk confides that someone is trying to kill him. Explaining that he has been condemned to die in three days, Monk claims that a man with a large black valise just large enough for a man's head has been following him, intending to decapitate him. Intrigued, Jack agrees to follow Monk and his bickering companion, Jean Anderson, as they leave the club. On a foggy sidestreet, Monk hears the footsteps of a man trailing him, and when Jean accuses him of hallucinating, he becomes agitated and attacks her. From the shadows, a peg-legged man with a deformed face appears, but Jack and Doc chase away the figure and then escort Monk home. On the way, Monk relates that he has just met Jean and that this wife Ellen is an invalid whose paralysis was predicted along with his death. At the house, Monk tells Jack and Doc about the mysterious oriental city to which he and Ellen journeyed one year earlier: Throughout the city's labyrinthine streets, Monk is haunted by an eerie melody played by a street musician. Upon returning to San Francisco, Monk hears the tune again, and when he questions the blind beggar who is playing it, the man leads him to an unfamiliar section of the city. In a deserted temple, Monk meets a man who calls himself "Mr. G" and claims that he is the High Priest of the Barokan, a Tibetian sacred society. After telling Monk that he has been trailing him for months, Mr. G reveals the mummified body of the group's founder, who bears a striking resemblace to Monk. Explaining that the founder's head is deteriorating, Mr. G offers Monk $10,000 for his head as a replacement and warns him that he has but one year to live. One month later, Monk decides to take Mr. G's prophesy seriously after a letter arrives at the house predicting his wife's paralysis and three days later, Ellen finds she cannot walk. Upon finishing his story, Monk leaves the room and Ellen confides to the detectives that she fears her husband is suicidal, feeling desperately guilty for her condition. The detectives then bid Ellen goodnight, and once alone in her room, Ellen stands and walks to the telephone to call her doctor. In the living room, Jack, meanwhile, asks to see the letter, and when Monk approaches his desk, he notices a new message, predicting his death in two days. Soon after, Ellen's physician, Dr. Han, enters the room and becomes apprehensive when Jack begins to question him. After Han exits, Jack surmises that the doctor is not Russian, as he claims, but a Eurasian who is involved in the miasma enveloping the Monks. Later, at the Samovar Club, Jack tells Doc that he has examined Monk's will and has learned that Monk's inheritance, valued at two million dollars, will be revoked if he ever divorces. Speculating that someone is trying to drive Monk to suicide in order to inherit his fortune, Jack proposes to use Monk as bait to trap his stalker. As Doc and Jack follow Monk that night, the peg-legged man lurks in the shadows until a woman's scream drives the man away. When the detectives hail a taxi to search for him, Jean steps out of the vehicle and admits to being the screamer. The peg-legged man, meanwhile, returns to his flat, and after he removes his hideous mask, a man steps from the shadows and slits his throat. The next day, Doc and Jack locate Monk at Dr. Han's office, and Monk claims that he walked the streets alone after the detectives disappeared the previous evening. Jack then shows him a newspaper story recounting the pegged-leg man's death and identifying him as Jean's father. From Han's office, Jack goes to visit Justin Reeves, a specialist in oriental artifacts. After questioning Reeves about his relationship with Ellen, Jack accuses him of being Mr. G and cautions him that there is no honor among thieves. Jack's warning proves accurate after Jean is murdered. Offering himself as bait to trap the killer, Jack proposes that the police issue a statement declaring that Jack knows the murderer's identity and then arrest him as a material witness. After the story appears in the newspapers, Jack escapes from jail and takes refuge in a warehouse owned by Monk. There, he instructs Doc to send telegrams to Han, Reeves, Ellen and her nurse, Miss Osgood, instructing them to assemble at the warehouse at midnight, and the anxious group meets later in Ellen's room. Reassuring them that Jack is bluffing, Ellen reminds them that they will soon be two million dollars richer and exhorts them to carry out their plans the next day. Everyone but Reeves then leaves the room, and Monk knocks at the door, sending Reeves scurrying behind the curtains for cover. Upon entering his wife's room, Monk claims to have heard a man's voice and insinuates that she is entertaining a lover. After Monk departs, Reeves, panicked, tries to flee the grounds, but is felled by an unseen assailant. Returning to Ellen's room, Monk boasts that he has just slit Reeves's throat and vows to make her suffer before killing her as well. Monk then hurries to the warehouse and informs Jack that he is the next to die. After Monk discloses that he learned about his wife's treachery by bribing Han, Jack smashes a piano lid on his hand and escapes. When Doc arrives soon after, Monk takes him hostage, but Jack overpowers him, and Monk then speeds away in a stolen car. Careening out of control, Monk smashes the car into a lamp post and loses his head. Returning to the present, Jack wonders out loud about what happened to Monk's missing head.