A Narrow Door by Joanne Harris

Now I'm in charge, the gates are my gates. The rules are my rules.
It's an incendiary moment for St Oswald's school. For the first time in its history, a headmistress is in power, the gates opening to girls.
Rebecca Buckfast has spilled blood to reach this position. Barely forty, she is just starting to reap the harvest of her ambition. As the new regime takes on the old guard, the ground shifts. And with it, the remains of a body are discovered.
But Rebecca is here to make her mark. She'll bury the past so deep it will evade even her own memory, just like she has done before. After all...
You can't keep a good woman down.

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