I think this movie sort of works

Most horror/thrillers were, thru the mid-'60s, mood piece/mystery films, and that's what this is.

I love the flavor of this picture, even if the script was perhaps a little lacking. But the execution was very competent (although the prologue scene seems stuck on and feels like it was shot by somebody else for a TV movie) from the montage-y windshield credits on.

Otherwise, the movie just sort of works. But then '60s thrillers just have something in them that's hard to define, and when the lead characters hop in a car and drive out to the boonies, the shrouded threats always seem believable somehow.

Another poster put it nicely when he said:

I wouldn't call The Shuttered Room a classic, but I think it's a terrific little film, and things that really impressed me upon seeing it again were the pleasure in seeing four super-fine performances (Young, Robson, but especially Lynley and Reed) again -- and also how I'd previously never consciously realized how extremely well-directed and photographed the film is. Just beautiful filmmaking. If anything, it's the writing that's the film's weak link, but the superlative casting, acting, direction and cinematography more than make up for that.