We Were Liars by E. Lockhart

Each summer, the Sinclair family clan gathers on an island off Martha’s Vinyard. Among them are three teenaged cousins, Cady, Johnny, Mirren, and a nephew of a family friend named Gat. They are close despite the fighting and excessive drinking of Cady’s, Johnny’s, and Mirren’s mothers and the manipulation tactics of their grandfather. All of that will change during “summer fifteen” when Cady wakes up with amnesia at the water’s edge, and she struggles to discover what happened and why no one will be honest with her. We Were Liars is an original story with a plot twist that will leave its readers stunned.