Sherlock Holmes sets out to discover why a trio of murderous villains, including a dangerously attractive female, are desperate to obtain three unassuming and inexpensive little music boxes.

Sherlock Holmes investigates when young women around London turn up murdered, each with a finger severed off. Scotland Yard suspects a madman, but Holmes believes the killings to be part of a diabolical plot.

Sherlock Holmes takes on a case that the press has dubbed the pajama suicides. Eminent men are going to bed in the safety of their own homes, with everything seemingly being normal, only to commit suicide in the night. Holmes fakes his own death in the hopes of giving him a freer hand in the investigation and is convinced that a woman, a female Moriarty as he describes her, is behind the deaths. The dead men were all eminent and very wealthy. He impersonates a wealthy retired Indian military officer in the hope of drawing out the woman and he soon meets Adrea Spedding but she quickly sees through his disguise and proves herself to be the challenge Holmes predicted she would be. She is a worthy adversary and soon traps him setting him up in a carnival shooting gallery that seems to assure his death.

Starting in Switzerland, Sherlock Holmes rescues the inventor of a bomb-sight which the allies want to keep from the Nazis. Back in London it sems that the inventor is not all that he seemed.