Harry thinks he's too old for his bucketful of dinosaurs but they have other ideas. He looked after them when he was little and now they're determined to stick by him . . . for life. And Harry is not the only one who's got a lot bigger! When a mysterious set of plastic dinosaur cards appear on his key-ring, Harry soon finds that he can call on an army of Back-Up Dinosaurs. It only takes a rub with his finger to call up some MONSTER-sized muscle! When Harry hears that Mr Oakley has been robbed by a nasty crook, he hopes that he and his friends - Jack, Charlie and Siri - can solve the crime. And after a night-time visit from a grateful Spinosaurus, Harry discovers that he now has a whole pocketful of back-up . . .