A frightened woman is murdered in the London apartment of a well-known novelist named Henry Leroux. The police arrest Leroux's butler, but he escapes and runs off to a mysterious opium den, the lair of a drug dealer named Mister King. Gaston Max, a detective from Paris, arrives in London to investigate the drug trafficking. Although the police take down the gang, Mr. King escapes and manages to keep his true identity a secret.