The Cliff House by Christopher Brookmyre

Jen’s hen party is going to be out of control. She’s rented a luxury getaway on its own private island. The helicopter won’t be back for 72 hours. They are alone – or so they think. As well as Jen, there’s the pop diva and the estranged ex-bandmate, the tennis pro and the fashion guru, the embittered ex-sister-in-law and the mouthy future sister-in-law. It’s a combustible cocktail, one that takes little time to ignite, and in the midst of the drunken chaos, one of them disappears. Then a message tells them that, unless someone confesses her terrible secret to the others, their missing friend will be killed. Problem is, everyone has a secret. And nobody wants to tell.