Teenager, Jason, and his friends, Bill, Becky and Liz, are recruited by an unusual messenger to pit their wits against an international gang of forgers, This gang is intent on destabilising the British economy by flooding the country with forged £20 notes which could pass off as the real thing. A number of problems immediately arise. The messenger has not first contacted the police, because the gang operate from an impregnable, moated castle, to which the police could not easily gain entry. Even with a search warrant, the gang would have ample time to destroy any incriminating evidence before they lowered the draw bridge. In any case, until the gang start to distribute the forged currency, the police have no evidence which would justify issuing a search warrant. The gang is well equipped with hi-tech machines. Jason and his friends, who are also technically knowledgeable, are able to secretly infiltrate the castle and outwit the gang.
