Sir James Blake has retired from Scotland Yard so that he can assist his niece Hope and her friend Jerry in developing an apparatus they have invented. Sir James thinks that their invention has the potential to prevent wars, and plans to donate it to the League of Nations. But a gang of criminals led by the elusive "Scorpion" steals the device, and Blake and his associates must recover the invention and determine the identity of the "Scorpion".

• Crime
• Mystery