Set over a long weekend in East Anglia, a surprise phone call from an old university friend, invites Ian and his wife for a few days by the sea. Their hosts, Ollie and Daisy, are a golden couple, and the scene is set for sunlit relaxation. Dangerous tensions quickly emerge from within the stifling atmosphere of a remote cottage in the hottest days of summer. Ominous revelations from Ian's past slowly intrude, and his rivalry with Ollie intensifies as they resurrect a long established and highly competitive triathlon. Each day becomes a series of challenged for higher and higher stakes, setting in motion actions that have irreversible consequences.