In the quaint village of Peterswood, a baffling crime sends the Five Find-Outers on a thrilling quest. When a mysterious thief with seemingly invisible powers strikes Hilary's own home, the children embark on a mission to uncover the truth. The clues left behind—a trail of enormous footprints, peculiar glove prints, and enigmatic torn papers—lead them to unlikely suspects. With Fatty's cunning disguises and the Find-Outers' sharp wit, they outsmart the bumbling policeman Mr Goon and inch closer to the elusive thief. As the culprit strikes again, targeting their own secret hideout and Mrs Williams' house, the mystery deepens: No one seems to catch a glimpse of the thief in action.