You can watch the trailer from TCM's website here.
A group of young, twenty-something Londoners (including American teen idol Frankie Avalon, then thirty, courtesy of the AIP connection) leave a swinging, booze-filled party to visit a haunted house out... in the woods, somewhere. One of the young mods is murdered, leading the others to suspect that someone among them committed the crime.
Your first instinct on hearing of this movie might be to laugh at it. It's not a great film, but it is interesting, so I recommend watching it at least once instead. Then you can laugh at it if you want. I didn't, though. There are seeds of a good suspense film in here, but due to circumstances beyond the control of director Michael Armstrong, the psychological horror film (with a touch of the Italian giallo film just then becoming popular) he was trying to make was mostly lost, though it's there in the unusual, ambiguous final scenes (easily the film's best). What looks at first to be a haunted house film turns out to be a suspenseful mystery as the group of friends (implausibly) decide to cover up their friend's murder and (after wisely leaving the house) determine which one of them is guilty of the crime, over the course of a week. The cover-up takes a emotional toll in the form of guilt and hallucinations, leading to a return to the murder scene.
That, from what I've read on the IMDB entry for the movie, is the film Armstrong directed, and it isn't bad. At some point, however, AIP brass ordered re-shoots with another director, leading to a subplot of one of the women of the group, Sylvia (Gina Warwick), attempting to break off her affair with a married man (George Sewell). The spurned suitor is shoehorned into the film as a suspect in the killings (in spite of the fact that the initial murder in the house takes place when the only entrance is firmly locked, and Sewell isn't inside. Whoops). The new footage also includes several police inspectors investigating the disappearance of the first victim. Not only do these scenes never interact with the main plot (the police investigation is never really resolved), but several of them were shot during an overcast day and inserted among scenes of the friends exploring the house at nighttime (whoops again!). The result is a film that often looks very disjointed, and every time the new scenes appear, the psychological suspense evaporates. Armstrong's scenes often include interesting visual effects meant to establish the emotional toll their friend's death and their cover-up is taking on the lead characters (in the form of zoom shots of things like gargoyles in architecture*), and there's an effective moment during the initial visit to the house when a reel-to-reel tape recorder finishes, leaving the tape end to flap quietly but persistently in the stillness. The new footage has none of these touches and never adds anything to the theme. And the first murder scene, which is surprisingly gory for a film of the time period, was reportedly darkened to obscure most of the bloodshed and secure a PG rating. (For a PG film of 1970, it's still quite bloody). The new scenes include two more murders which are so oblique and bloodless I wasn't sure, watching one of them, if the character was actually dead (I had to real the reviews in the IMDB entry to figure it out). This is another reason why the films looks so disjointed.
Aside from being a suspense film, Horror House is also a neat time capsule of Swinging London circa 1969, though I guess you could argue that London wasn't quite so swinging by then and the film feels a couple of years out of date. (The music you hear is a mix of 1967 pop and heavier 1969 rock - there's even a groovy scene with a jazz-rock(!) instrumental group in a hip nightclub). The guys wear scarves and mod shirts (except for Frankie, who mostly sports turtleneck sweaters), and the girls wear miniskirts and boots (and how), and pile up their hair. There are a few scenes in the real Carnaby Street, so you get to see a few of the hip boutiques of the time (in the "new" footage, you also get quite a few shots of suburban England, which looks anything but hip). The not-so-wild party is set in a flat with posters of Brando, Buster Keaton, and a psychedelic Mothers of Invention. I remember a Che Guevara poster turning up somewhere as well. The "haunted" house (sorry, I don't think I'm spoiling anything at this point by mentioning it isn't) is effectively barren and provides some good atmosphere - it's a real house, not a stage set. The film opens and closes with soft shots of candles seen from a distance; it's an interesting way to frame the film (and the closing shots add to the film's moody ending).
Turner Classic Movies screened this film last night as part of their Underground series (along with a ten-minute short, from 1941, on the dangers of washing clothes with gasoline - a burning issue back then, I guess! Pardon the pun. The short opens with several shots of stock-footage explosions. Who knew laundry could be so destructive?).
(*the film includes quite a few zoom shots - scenes where a camera views a large area, such as a city block, before closing in on a small detail, such as a piece of architecture. This type of camera movement turns up in many 70's films I've seen - the close-cutting of it's day, I guess)
