Whispers have reached Scotland Yard of an elusive figure that has appeared on the dark horizon of crime and is making its influence felt. Then the first threatening letter comes, demanding a huge payment, or death for its recipient. The victim goes to the police for protection - only to be promptly murdered. The same graft has been worked by gangsters in Chicago - and now it seems they have arrived in London. As Scotland Yard strives to find the criminal mastermind responsible, so too does a mysterious woman...the Lady of Doom!