Jealous of her sister's fling with Gilles, Claude locks her in her room one night so she can have him all to herself. She quickly falls in love with him, even after his shady past as a convicted rapist is uncovered. And even after he attempts to strangle her right after this past is uncovered. Meanwhile, a black-clad killer is stalking the nearby farmlands, dispatching blonde-haired blue-eyed lasses, and removing said blue eyes as some kind of twisted trophy.
Finally, Gilles's past is uncovered by the local fuzz, and he takes flight with Claude in tow. Deciding that she's slowing him down/doesn't deserve to share his burden (it's tough being a convicted rapist), he knocks her out and makes a solo break for freedom. Meanwhile, Nicole has discovered a secret room somewhere which reveals the secret of the killer's true identity. Will she escape and be able to alert the authorities? No, course not.
Gilles is far from the only character who's nursing a secret (little pun there), and, as more and more dirty historical laundry is aired in public, we finally learn the truth behind the truth behind the blue eyes-obsessed killer.
And, as usual, he casts himself in a role which, in a world in which he had less creative control, would've probably been played by a handsomer man. This is a particularly egregious example of this, because Gilles represents an inversion of the trope of the sexually alluring, mysterious woman arriving in a town/home and seducing her way through everyone like a hot knife through butter (think Edwige Fenech in Your Vice is a Locked Room.., to give but one example). These characters tend to be fantasy figures, the male writer's' and directors' wonderment at the mystery of female sexuality personified in a neat little sexy package. In this case, the wonder is how so many women consider the little package of Naschy (I'm referring to him as a whole here; I have no idea how big his penis is) to be so sexy.
But consider him sexy they do, even when the truth about his mysterious past outs, and he tries to strangle you and then admits that he constantly has fantasies* about strangling women. This is fairly typical of Naschy; he seems to like playing flawed, to say the least, 'heroes'. It's often difficult to discern whether we're actually supposed to identify, or at least sympathise, with his characters, with Gilles being no exception. Does he enjoy playing shits, or is he allowing his dark side space to breathe, and attempting to imbue his darkest impulses with a dash of humanity, to 'normalise' them in some way? The good news is that there's always enough going on elsewhere in his films (often involving secondary characters also played by Naschy) so that you don't have to worry too much about whether you like his main guy or not. And, whatever else you feel about Gilles, you should surely pity his complete inability to function under pressure, as evidenced by the way in which he chooses to run-through deep snow, no less-right across the line of fire of a police sniping squad, rather than take advantage of the ample tree cover on offer and move away from the threat.
Giallo-wise, you get a kind of mixture between the classic black-gloved killer and the familial cod-psychological warfare from the Lenzi school. In fact, until the first murder scene elbows its way to the fore after about 40 minutes, you'd be forgiven for thinking that the whole film is going to revolve around the clandestine interactions of Gilles and the sisters. But once the murderer has a taste for blood they strike again and again, in rapid succession. These scenes aren't exactly top drawer in terms of style, but they do incorporate an interesting musical element-a reworking of Frere Jacques**, which proves to be of relevance to the plot.
The solution to the plot-the murder plot-is actually flagged fairly clearly early on, in a way which many viewers might write off as a lazy attempt at generating some red herring-y misdirection. There is a double-twist ending-both 'twists' of which are foreshadowed-which is handled pretty well, but there's no real investigative through line; there's just too much going on to allow for a focus on one character's sleuthing. Not to mention, there's not a whole lot of sleuthing needed; it's more a question of lining the suspects up against the wall and figuring out possible motivations than following clue after clue.
The mastermind is indeed caught through deductive reasoning, rather then incontrovertible proof, although given that the police are heading the investigation, some tangible evidence is nonetheless required. If we're to believe the local bobby, this 'evidence' is in the form of a letter written by a character, in which she says mean things about the mastermind. I'm guessing the Spanish legal system had a broader definition of what constituted proof back in the early 70s. Given that it was the legal system of a fascist dictatorship, I suppose this may well have actually been the case.
So, all in all it's not a brilliant film, but there is much to enjoy. There are tits for the lads (Naschy gets his hands on a couple of extra-milky ones early on), and some sweaty, topless Nasction, if you're possessed of the same quirky proclivities as the (to be fair, largely psychotic) sisters. The theme tune is bizarrely bad, but it does nonetheless seem to endearingly say 'don't worry about all this; it's just a bit of a lark, scored with some pretty poor choones'. If your giallo tastes don't extend far beyond the Italianate, you may not find much here. If you're open to a bit of paella on your spaghetti, though, you should have a bit of a lark, if you can ignore the pretty poor choons (not Frere Jacques though; that's a stone-cold classic). And, when it's all over, see if you can figure out which early 70s effort from his mortal enemy Jess Franco was (perhaps unconsciously, or unwittingly) being ripped off by Pablo Nasch. See what I meant earlier? All these paragraphs, and I've only mentioned the film's director once. Sorry, Carlos Aured (twice now!).
PS Animal lovers beware; there's a particularly harrowing scene of a pig having its throat slit. It's pretty much how pigs were butchered at the time, and no doubt the flesh of the beast went to a good home/homes, but it's nonetheless pretty shocking to witness, 'helped' by some heart-wrenching soundtrack squeals. The scene is in some ways totally gratuitous, as it serves mainly to introduce a character who's murdered in the very next scene, but there is a subtext running through the film which seeks to equate the characters, especially Naschy's, with animals. Which is fine, and pretty well incorporated, but I personally could've done without seeing an animal suffer onscreen in service of this subtext (I prefer my animals to suffer behind closed doors, so I don't feel bad about eating them).
*These fantasies, which were filmed on a soundstage dressed in nothing but red light and smoke, have a bizarre, minimalist quality. In some ways, they're the least giallo-ey thing about the film, in that they scream low budget Spanish film (or low budget Brazilian; one could easily imagine Coffin Joe tagging in for Naschy).
**The film is set in France, despite the cast and crew being overwhelmingly Spanish. I can't really put my finger on any concrete reason for setting the film over the border, apart from the dose of exoticism which any 'foreign' location, no matter how rustic and earthy, provides.