 Mr. Verloc, a cinema owner, is part of a gang of saboteurs in London. He lives with his wife, Sylvya, and her young brother, Stevie. They know nothing about Verloc s secret. Scotland Yard assigns an undercover detective, Ted, to work in a shop near the cinema and investigate the man. The head of the gang assigns Verloc to put a bomb in the metro. The man sends Stevie there with the "bag".