Set in the title manse, this chilling comedy chronicles the spooky exploits of a Yankee car salesman working in London who sets out to deliver a car to a remote and very creepy Welsh estate. Unfortunately he discovers the owner dead. While attempting to leave a fierce storm erupts and he has a wreck. He returns to the mansion to seek shelter from the disparate sisters therein. Once warm and dry, he meets the rest of their strange family, including twins, a looney who is building an ark, and the matriarch of the household. The storm rages on and as the grim night slowly passes, family members are bumped off at appallingly regular intervals leaving the American to solve the crimes..