Can the entire course of a life be traced back to a single moment? On a coveted two-week beach vacation, working mom Kate Baker’s nine-year-old daughter, Olivia, vanishes suddenly among the waves—a heart-dropping incident that threatens to uproot her entire reality. But in the next moment, Olivia resurfaces, joyously splashing. What would I do if she didn’t come up? Kate wonders. How would I live without her? In another set of circumstances that hold a different fate, Kate doesn’t have to wonder. Because in that “other” world, in the pulse-pounding seconds after Olivia goes under, she doesn’t come back up. Told in parallel timelines, Kate begins to live two lives—one in which Olivia resurfaces and one in which she doesn’t. In the reality that follows her daughter’s death, she maneuvers through every mother’s worst nightmare, facing grief, rage, and the ques­tion of purpose in the aftermath of such profound loss. She endures, day by day, in a world without her daughter. In her alternate timeline, while she explores a tremulous romance with her best friend, Jason, she finds herself grappling with the ex-husband who abandoned Kate and Olivia years prior.