On Yorkshire's gradually-crumbling mud cliffs sits an Edwardian seaside house. In the bathroom, Jacob and Ella hide from their parents' passionate arguments by playing the 'Underwater Breathing' game - until the day Jacob wakes to find his mother and sister gone.

Years later, the sea's creeping closer, his father is losing touch with reality and Jacob is trapped in his past. Then, Ella's sudden reappearance forces him to confront his fractured childhood. As the truth about their parents emerges, it's clear that Jacob's time hiding beneath the water is coming to an end.