We Were Liars by E. Lockhart
In her fifteenth summer at her family's place on an island off the coast of Massachusetts, Cadence Sinclair suffers a head injury that leaves her with migraines and memory loss. Two years later she and her cousins Mirren and Johnny, as well as Gat Patil, a family friend, try to piece together her memories from the last two years in order to solve a family mystery dealing with the Sinclair family fortune.
Review from School Library Journal Starred:
Cadence Sinclair Easton comes from an old-money family, headed by a patriarch who owns a private island off of Cape Cod. Each summer, the extended family gathers at the various houses on the island, and Cadence, her cousins Johnny and Mirren, and friend Gat (the four "Liars"), have been inseparable since age eight. During their fifteenth summer however, Cadence suffers a mysterious accident. She spends the next two years—and the course of the book—in a haze of amnesia, debilitating migraines, and painkillers, trying to piece together just what happened. Lockhart writes in a somewhat sparse style filled with metaphor and jumps from past to present and back again—rather fitting for a main character struggling with a sudden and unexplainable life change. The story, while lightly touching on issues of class and race, more fully focuses on dysfunctional family drama, a heart-wrenching romance between Cadence and Gat, and, ultimately, the suspense of what happened during that fateful summer. The ending is a stunner that will haunt readers for a long time to come.