I Capture the Castle by Dodie Smith

Cassandra Mortmain lives with her bohemian and impoverished family in a crumbling castle in the middle of nowhere.

Her journal records her life with her beautiful, bored sister, Rose, her fading glamorous stepmother, Topaz, her little brother Thomas, and her eccentric novelist father who suffers from a financially crippling writer's block.

However, all their lives are turned upside down when the American heirs to the castle arrive and Cassandra finds herself falling in love for the first time.

'I know of few novels that inspire as much fierce lifelong affection in their readers' Joanna Trollope