In a canoe trip gone terribly wrong, the little girl that 17-year-old Lark babysits and the boy Lark is dating fall into the lake at the same moment. They are both drowning, and Lark can only save one of them in time. In this critical moment, Lark's world splits into two, and the rest of the novel takes us, in alternating sections, through the consequences of both choices. In one life, Lark and Alec are falling in love while Annabelle is hospitalized in a coma. In the other life, Annabelle is alive and well while Alec is at death's door. Lark's malfunctioning phone delivers messages from one life to the other, but it takes Lark a while to piece together what's going on. She needs to get back to the beginning, and complete a choice, to make her world whole again.