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".
| Actor | Role |
|---|---|
 Ralph ByrdJerry Sheehan | Jerry Sheehan |
 Joan BarclayHope Mason | Hope Mason |
 Lloyd HughesDoctor Marshall | Doctor Marshall |
 Dickie JonesBobby Mason | Bobby Mason |
 Lucille LundDuchess | Duchess |
 Nick StuartJulot | Julot |
 Sam FlintChief Insp. Henderson | Chief Insp. Henderson |
| GGail NewburyMimi - Policewoman | Mimi - Policewoman |
 Jimmy AubreyThe Hag / Baron Polinka | The Hag / Baron Polinka |
 Theodore LorchDaggett - the Butler (as Ted Lorch) | Daggett - the Butler (as Ted Lorch) |
| GGeorge DeNormandPedro - Henchman | Pedro - Henchman |
 Bob TerryPeyton - Henchman | Peyton - Henchman |
| WWilliam FarrelCount Basil Segaloff | Count Basil Segaloff |
| FFrank WayneCharles - the Footman | Charles - the Footman |
 Dick CurtisNicky | Nicky |