From his Brazilian underground fortress, which is protected by a group of dacoits, archvillain Fu Manchu dispatches 10 native women, each injected with a deadly snake poison, to give their kiss of death to Fu Manchu's enemies, among them some of the world's most powerful figures. Celeste goes to London to assassinate Fu Manchu's longtime rival, Inspector Nayland Smith of Scotland Yard, but she succeeds only in blinding him and is run down by a truck while attempting to flee. As Inspector Smith and his colleague, pathologist Dr. Petrie, prepare to go to South America to find a cure for Smith and to destroy Fu Manchu, the archvillain turns his attention to renegade bandit and gang leader Sancho Lopez. Fu Manchu captures him and through torture extracts the bandit's promise to kill Smith. The treacherous Fu Manchu sends Carmen, who has been injected with the snake poison, with Sancho; her instructions are to kill Sancho once he has killed Smith. Carl Jansen, an undercover agent for Smith, joins Ursula, a nurse ministering to the natives, and they rendezvous with Smith and Dr. Petrie to decide how to destroy Fu Manchu. Carl, Dr. Petrie, and Ursula set off into the jungle, leaving Smith behind. Ursula and Dr. Petrie are captured by Sancho and taken to Fu Manchu's underground headquarters, but Carmen frees them. Ursula, Dr. Petrie, and Carmen hurry back to Smith when it is learned that Carmen's blood may contain an antidote with which to cure Smith's blindness. A transfusion is effected; Smith is cured; and he and Dr. Petrie return to the underground fortress to rescue Carl, who, having rigged the fortress with dynamite charges, has been overpowered by dacoits. Smith frees Carl, and they and Petrie light the dynamite charges. A series of explosions destroys the fortress, but from the rubble comes the voice of Fu Manchu promising that the world will hear from him again.