Set over a long weekend in East Anglia, this is the chilling story of a rivalrous friendship - as told with deceptive casualness by the narrator, Ian. It opens with a surprise phone call from an old university friend, inviting Ian and his wife, Em, for a few days by the sea. Their hosts, Ollie and Daisy, are a golden couple, and the scene is set for sunlit relaxation.

But dangerous tensions quickly emerge, and in the stifling atmosphere of a remote cottage in the hottest days of summer, Ollie and Ian resurrect a bet made twenty years before. Each day becomes a series of challenges for higher and higher stakes, setting in train actions that will have irreversible consequences.