Andres (José María Guillen) and Ana (Mariana Karr) are a young couple who are expecting their first child after what seems like an awful long time trying. It's the weekend, so they decide to go out, but are not sure what to do; after leaving their cosy apartment, a trip to see Star Wars is in order, and then they and their pet Alsatian Blackie set off for somewhere to eat. However, as they drive through the city, they notice another young couple trying to attract their attention. Ignoring them at first, they are forced to concede that these strangers seem to recognise them, and are made to stop by the other couple's car. They both get out and introduce themselves as Bruno (Ángel Aranda) and Berta (Sandra Alberti) - but who are they really?
Well, Satan's Blood didn't really begin like that, it started with five minutes of Devil worship as the "priest" pleasured himself with a nubile human sacrifice before ending her life for Beelzebub, an arresting beginning that didn't seem to have much to do with the rest of the movie. This was ostensibly directed by Carlos Puerto, more commonly a screenwriter (he had those duties here), but one look at the other name in the production credits would reveal the telling presence of Spanish trash merchant Juan Piquer Simón as producer, but secretly co-director into the bargain. Any seasoned horror fan would immediately be aware this indicated something special, if not in the realms of general excellence.
So it was with this, an absurd but full-blooded sex horror which focused on a small cast of four for most of its comparatively brief running time, as Andres and Jenny Agutter looky-likey Ana are practically ordered to accompany Bruno and Berta back to their place, which turns out to be an isolated mansion out in the Spanish countryside. The longer the evening goes on, the further it appears the innocent couple are at the mercy of the decidedly more worldly couple who are manipulating them to make sure they're not going anywhere, no matter how much they would like to leave. Oh, you can't go now, it's too late and there's a storm and you would need us to show you the way anyway and... you get the idea, they're trapped.
For a plot that was basic in many aspects, the filmmakers certainly packed in plenty of incident, though the hint that all was not as it seemed came when Ana interrupts Berta in the kitchen where Berta has been stuffing her face with raw meat of unknown origin. Pausing to wipe away the blood from her lips, she assures her all is well, in a film like this shorthand for "Get out while you can!" and before they know where they are, Andres, who has been baffled that Bruno has photographic evidence they were at school together, and Ana are participating in a séance that reopens old emotional wounds. As if that were not enough, once they retire to bed Ana has reason to venture downstairs in the middle of the night and is nearly raped by a handyman for her curiosity, though she fights him off.
Then we reach the part that stuck in the minds of anyone who saw it as Andres helps out his wife by investigating the house, only to find their hosts holding a Satanic ritual in the lounge which somehow, apparently under a trance, the two innocents are moved to participate in, in effect meaning everyone gets naked and greased up and a lusty foursome ensues with lots of surprisingly explicit, though softcore, combinations. Maybe not that surprising when you are aware Spanish cinema was embracing the loosening of censorship restrictions in the seventies, and Satan's Blood is often held up as a prime example of that once General Franco had expired, but the truth was the national exploitation movement in movies had been moving in that direction even when he was alive. This was leading up to a nonsensical set of twists that though far from sensible were also far from dull, capitalising on the nightmare logic horror movies were trending on during this decade, so, no, this wasn't a classic by any means, but you may well find yourself enjoying its outrageousness. Music by Librado Pastor.