One perfect summer day, mother of two Alice walks into the sea ... and never returns. Her daughters - loyal but fragile Lily, and headstrong, long-absent Marietta - are forcibly reunited by her disappearance. Meanwhile, with retirement looming, DI Fox investigates cold cases long since forgotten. And there's one obsession he won't let go: a tragic death twenty years before. Can Lily and Marietta uncover what happened to their mother? Will Fox solve a mystery that has haunted him for decades? As their stories unexpectedly collide, long-buried secrets will change their lives in unimaginable ways.