Surrounded by the Blackwater estuary, The Stanhope hotel sits on a beautiful remote island. Tonight is the grand reopening, and organiser Hannah watches the guests with pride. But as drinking descends into debauchery, drunken revellers wade into the water, unaware of the treacherous tide at The Drowning Hour. They are never seen again. Tormented by a terror of water, Hannah is stuck on the island over winter. Whispers about That Night begin to circle. Someone knows what really happened in The Drowning Hour - and Hannah isn't safe...