Diamonds and Rust by Jane Thompson

Alice Morrison has created a world for herself. The headmistress of a girls' private school she lives surrounded by books and her beloved cat, Orlando.

Not a very exciting existance - but a safe one. Until Mattie comes barrelling back into her life. Mattie, who she fell in love with when they were at school together. When Alice was the teacher and Mattie was the pupil, and Alice thought it would be forever.

But Mattie does not believe in forevers. Nor does she believe in safety. Given the chance she will create havoc in Alice's carefully constructed ivory tower. But this time it will be different and at the end of Mattie's stay no one will be untouched by the events set in train by her arrival...