Pearl and Jodie are sisters. Pearl is the quiet, cautious, studious one. Jodie is bold and brash and bad - but Pearl adores her anyway.
When their parents get new jobs as the cook and caretaker at a fusty old boarding school, the girls have to move there and spend their summer holidays in the school with just a few children and staff for company. And when they arrive, things start to change. Jodie has always been the leader - but now it's Pearl who's making new friends, like the amazingly tall, badger-watching Harley and Mrs Wilberforce, the wife of the Head who's confined to a wheelchair but introduces Pearl to wonderful new books.
Jodie just seems to be getting into more and more trouble - arguing with Mum, scaring the little children, flirting with the gardener...When term begins, their strange summer is over.
But things keep on changing. Jodie really doesn't fit in with the posh teenagers at the school.
But Pearl is doing well in lessons and has even more friends.
Maybe she doesn't need Jodie as much as she used to.
But Jodie needs her. And when the school celebrations of Firework Night come around and a tragic event occurs, Pearl realises quite how much she does need her big sister...