I searched for Plaisir à trois purely so that I could tick it off in my copy of The Aurum Encyclopedia of Horror, but all I could find was a French version of the film with no subtitles. Still, this being a typically trashy Jess Franco sadean sleaze-fest - 99% nudity and sex and 1% plot - it was easy to get the general gist of things.
Alice Arno plays Countess Martine de Bressac, who returns home after spending a year receiving psychiatric treatment for castrating one of her lovers. It's not long before Martine is back to her old ways, adding new exhibits to her torture dungeon: prostitutes that she and her husband Charles (Robert Woods) paralyse and subsequently display as human trophies. After spying on their sexy neighbour Cécile (Tania Busselier), Martine and Charles lure the young woman into their world of perversion.
Here's a catalogue of the sleaze on offer...
With the help of her manservant Mathias (Franco regular Howard Vernon), Martine picks up a hooker, draws her naked, then takes her to her dungeon to flog her.
Cécile rolls around sexily on her bed while Martine and Charles get fruity with each other (this happens twice).
The countess flogs mute sex-slave Adèle (Franco muse Lina Romay).
Martine shares a bath with Cécile.
The characters play a game where each must perform a sexy act: the countess does a striptease, Adèle makes out with a mannequin, Cécile has a lesbian romp with Adèle, and Charles humps Cécile (a scene that verges on hardcore).
The film ends with Charles, Martine and Adèle taking Cécile to the dungeon, where the tables are turned on the countess: instead of adding Cécile to her collection, Martine finds herself being administered with the paralysing injection instead.
With a notable lack of underwear, loads of full frontal female nudity, a hunchbacked dwarf, crash zooms aplenty, a jazzy lounge soundtrack, and some really bold fashion choices from Charles (purple suede suit with yellow shirt, and a two piece that looks like it's made from floral upholstery material), this is bound to please avid Franco fans but will probably bore most people silly.
As for it being horror... I really don't think so.
3.5/10, rounded up to 4 for IMDb.