Family of Liars by E. Lockhart

A windswept private island off the coast of Massachusetts.
A hungry ocean, churning with secrets and sorrow.
A fiery, addicted heiress. An irresistible, unpredictable boy.
A summer of unforgivable betrayal and terrible mistakes.
Twenty-seven years before the events of We Were Liars comes another summer, another generation, and the secrets that will haunt them for decades—a story that is scandalous, tragic, and layered with mystery.
Welcome back to the Sinclair family.
They were always liars.