An excellent mystery by the bestselling author Enid Blyton, perfect for fans of the Secret Seven. Pip discovers that a room in Mrs. Crump's old empty house is not empty at all - someone has been using it! It's the perfect mystery for Fatty to use his new talent for disguises. Now it's up to Fatty and Pip, along with Bets, Larry, Daisy, and the dog Buster, to find out who has been using Mrs. Crump's old house. First published in 1945, this edition contains the original text and has no illustrations.