Bonnie and her timid cousin Sylvia are left in the lonely halls of Willoughby Chase when Bonnie's parents, Lord and Lady Willoughby, travel overseas. They are alone apart from the servants and the ravenous wolves which prowl about the grounds. But an even more dangerous predator lurks in the wintry darkness... Slighcarp the sinister new governess arrives with her greedy accomplice, Grimshaw.

Lord and Lady Willoughby are reported missing, believed drowned at sea, and Slighcarp's reign of terror gets underway. The children fight back but are sent to the terrible orphanage of Blastburn, where they are held at the mercy of the evil Mrs. Brisket.

Aided by the wild boy Simon, the girls risk a breathtaking escape through thick snow and dense forests, back to the safety of Willoughby Chase. But Slighcarp and the wolves are waiting...