A powerful storm rages through the Welsh mountains, driving three travelers off the road. Philip Waverton, his wife, Margaret, and their friend Roger Penderel are desperate to get out of the torrential downpour. Their only option is a mysterious old mansion, home to the bizarre Femm family and their brutish butler, Morgan.
Although the Femms have plenty rooms in their home, they are hesitant to allow guests to stay in them. Instead, Penderel and the Wavertons must settle in for the night by the ground-floor fireplace and hope the storm will pass by morning. But as the hours go by, their situation only gets worse. The storm intensifies, and the dark house begins revealing its secrets—like what lies behind the two locked doors on the top floor. Now the travelers can only pray they survive until morning . . .