Jimmy Stoker's dreams have been full of tigers since he started his Saturday job at the zoo. Boris the great Siberian tiger has died and rumours abound about what's going to happen to him now. Jimmy hears that someone wants to steal Boris's bones and when he sees the tiger's body being smuggled out of the zoo, he fears the worst with the help or sometimes hindrance, of his schoolmate, Billy, and the kind assistance of his old friend, Major Gregory, Jimmy is determined to investigate.