When PC Goon's nephew, Ern, comes to Peterswood full of ideas of detecting, the Five Find-Outers think up a first-class mystery, complete with clues, and send both Ern and Mr Goon off on a wild-goose chase to Christmas Hill.
But Ern loses his way and suddenly stumbles into what the Find-Outers are sure is a real mystery. Once again they are on the trail of a really thrilling puzzle, but Fatty's love of disguises lands both him and Ern in a very tricky situation.
