A quiet lakeside resort in Vermont seems like the perfect summer getaway for Olivia and Harry Somerville and their three young boys. But in a single moment, their idyllic family retreat becomes a mother's worst nightmare. Returning from a solo hike one afternoon, Olivia learns from a passing stranger that one of her sons has drowned--but not which one. In that moment, Olivia makes a panicked decision that will change her family forever. She runs. Olivia begins a new life in a quiet town, hiding in a lie she tells herself every day: "I have three children." If she never knows which son has drowned, can Olivia convince herself that none of them have? By shielding herself from reality, can she continue to live in a world where all three boys are still alive?