Six hours. One marathon swim. That's all Tully Birch needs to get her life straightened out. With the help of her best friend, Arch, Tully braves the waters of Lake Tahoe to break the record for the youngest person ever to complete the famous "Godfather swim." She wants to achieve something no one in the world has done, because if she does, maybe, just maybe, her mom will come back. The swim starts off well - heart steady, body loose, Arch in charge of snacks as needed. But when the swim turns dangerous, Tully fights for her survival. Does she keep going and risk her own safety and Arch's? Or does she quit to save them both, even if it means giving up hope that her mother will return?