The film is set in London. Fu Manchu (Warner Oland) is thought to have died 20 years ago, wrongly believing that Sir John Petrie (Holmes Herbert) was responsible for the death of his family during the Boxer Rebellion. He swore revenge on Sir John and his family. Princess Ling Moy (Anna May Wong) is a celebrated exotic dancer who goes to the house of her agent Morloff (Nicholas Soussanin) to finally see her father, whom has she never met. Morloff is one of Fu Manchu's henchman, and Fu Manchu is Ling Moy's father. Ah Kee (Sessue Hayakawa), a Chinese detective working with Scotland Yard tells Sir Basil Courtney (Lawrence Grant) that Fu Manchu is still alive and he has just seen him. Sir Basil realizes Fu Manchu will try to murder Sir John, but is unable to warn him by phone because the wires were cut. Sir Basil and Ah Kee go to Sir John's home, which is next door to Morloff's house.Sir John Petrie receives a threatening letter from Fu Manchu, who then appears in his study. Fu Manchu drugs and hypnotizes Sir John, and then kills him in front of the Petrie family and police. Ah Kee shoots Fu Manchu before he can kill Sir John's son Ronald (Bramwell Fletcher).The mortally wounded Fu Manchu escapes and meets Ling Moy, making her take an oath as his son to avenge his and their family's deaths. To remove suspicion from her, Fu Manchu apparently attempts to kill her. They are found and he is shot dead by Ah Kee. The police, Ah Kee and the Petrie family are unaware of the link between Fu Manchu and Ling Moy.Ling Moy befriends Ronald, intending to kill him, yet they start to develop a romantic interest despite his engagement to Joan Marshall (Frances Dade). Ah Kee is also attracted to her, although he is only delegated to guard her.Ling Moy finds she is unable to kill Ronald as she loves him, and the henchmen are unhappy with her not acting as the son she had declared to Fu Manchu she would be. She attempts to kill herself but is prevented. A henchman burns the incense of repentance, and she is persuaded to overcome her reluctance to kill Ronald. First she must deal with Ah Kee, whom she charms. He confesses his love for her and tries to persuade her to go to China with him.Joan is kidnapped and, while Ah Kee is occupied, Ronald Petrie and the police are lured to Limehouse to find her. Ronald is captured and brought to Morloff's house where Joan is actually imprisoned. Ah Kee discovers Ronald is in the building and realizes Ling Moy is duping him, and refuses to drink wine he knows is poisoned. Ling Moy reveals that she is the daughter of Fu Manchu. Ah Kee is tied up and locked in the attic.When Ronald hears Joan's screams, he rejects Ling Moy's advances, and she reveals her true identity to him. She declares Ronald must have a thousand bitter tastes of death before he dies, and prepares to have Joan disfigured with acid before he is killed. Ling Moy even tries to coerce Ronald into stabbing Joan to death. Ah Kee escapes, falls from the attic to the ground and is able to alert the police, who raid the house. Ronald and Joan are saved, and Ling Moy escapes. She is caught but attempts to kill Ronald. She is shot dead by Ah Kee, who declares his love for her before expiring at her side.