Book 1 of the Demon Headmaster
When Dinah is fostered by the Hunters she thinks her biggest problem will be fitting in with her foster-brothers, Lloyd and Harvey. However, once she starts at her new school it's clear that there's more to worry about. All the children, apart from a handful including Lloyd and Harvey, are too well-behaved - robotic almost - and oddly keen to please the creepy headmaster.
The three children set out to discover the nature of his influence over everyone . . .
but then Dinah finds herself saying and doing things she has no power over. Soon they uncover the headmaster's wicked plan. Controlling the school is just a practice run.
Gilian Cross