During a canoe trip with her boyfriend, Alec, seventeen-year-old Lark sees four-year-old Annabelle drowning in the lake. Alec is gravely injured as he jumps in to save the girl and Lark knows that she can only save one. The split-second decision splits her in two, with the rest of the novel tracking the consequences of Lark choosing Alec or choosing Annabelle.