Family of Liars by E. Lockhart

The prequel to We Were Liars takes readers back to the story of another summer, another generation, and the secrets that will haunt them for decades to come. 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. Welcome back to the Sinclair family. They were always liars.