"The Shuttered Room" is a 1967 British psychological horror movie ostensibly based on an HP Lovecraft story. It's about a couple, with a wide age gap, who move back to the lady's childhood home on a remote island to visit the old mill she's due to inherit. The locals however, do not intend to make her feel welcome. Aside from Oliver Reed, who instantly needs to do the mad nasty with youthful wife Susannah.
Oh and there's a monster in the attic. But, y'know, whatever.