Thirty-four-year-old marine biologist Kyra Winthrop remembers nothing about the diving accident that left her with a complex form of memory loss. With only brief flashes of the last few years of her life, her world has narrowed to a few close friendships on the island where she lives with her devoted husband, Jacob. But all is not what it seems. Kyra begins to have visions—or are they memories?—of a rocky marriage, broken promises, and cryptic relationships with the island residents, whom she believes to be her friends. As Kyra races to uncover her past, the truth becomes a terrifying nightmare.