A gang of criminals has established a far reaching racket in counterfeit coins, making English gold sovereigns to order. The CID is kept busy, but then there's a mysterious epidemic of deaths from snakebites. Chief Inspector Dawson of the Metropolitan Division's scientific branch discovers the relationship between deadly snakebite and counterfeit coins. Dawson is aided by Detective-Sergeant Harriday and Gwenda Blane. But Dawson and his colleagues risk their lives attempting to smash a ruthless homicidal racket...