"Gravely ill." The haunting words keep repeating themselves over and over in Johnny Dixon's brain. After all the tests, doctors still can't find any earthly reason why Johnny's father lies unconscious. Could it be that Johnny's tangles with a malevolent creature have caused his father to be its latest victim? To save him, Johnny and his friends Professor Childermass and Fergie Ferguson must not only enter into battle with the fearsome fiend, they must fight it in the realm of its own unearthly world!