While out on an afternoon drive, electronics repairman Andy (José María Guillén) and his pregnant wife Annie (Sandra Alberti, DEATH SURROUNDS MONICA) meet Bruno (Angel Aranda, PLANET OF THE VAMPIRES) and Mary (Mariana Karr) at a traffic light. Bruno claims to be a school pal of Andy's, even though he is about ten to fifteen years older, and the younger couple find themselves invited to the older couple's house deep in the countryside (a house recognizable to Spanish horror fans from a number of Paul Naschy films). After dinner conversation turns towards the older couple's interest in the occult - which should have been a big red flag - and spin on the Ouija board that predicts Bruno's untimely death and accuses Annie of still being in love with Andy's brother. The gathering storm means that Andy and Annie will have to stay the night. When Annie gets up to let the dog inside, she is nearly raped by the couple's handyman. Andy and Annie confront Bruno and Mary and are drawn into a Satanic orgy, the aftermath of which spirals into a nightmarish whirlpool of murder and suicide.

After the death of General Franco, Spain eased up on its censorship standards (in the early seventies, the nudity and gore for which Spanish horror films are known only appeared in the export prints and not the domestic versions). The introduction of the "S" classification for films with gory and violent content lead to an exploitation film production boom from the mid seventies to the early eighties with sometimes near-pornographic content (this relaxation in censorship also lead to the return of Jess Franco to Spanish filmmaking after more than a decade exploring his unique brand of erotic horror in France, Germany, Portugal, and anywhere Harry Alan Towers or Erwin C. Dietrich could strike a deal). Director Carlos Puerto had directed a few shorts in the sixties, and wrote SATAN'S BLOOD producer Juan Picquer Simon's FABULOUS JOURNEY TO THE CENTER OF THE EARTH. Puerto found more work during this late seventies exploitation boom, penning Leon Klimovsky's gory TRAUMA and directing Paul Naschy in EL FRANCOTIRADOR/THE SNIPER. SATAN'S BLOOD was reportedly co-directed by Simon (and Librado Pastor's main title theme pops up on the Spanish track of Simon's slasher PIECES), who also is credited with the unique art direction. Like SEXO SANGRIENTO, another "S" classification picture, SATAN'S BLOOD seems as though it could have been more effective as a horror short without the nightmare logic padding; however, the end product has enough sex and creepy imagery to entertain seasoned Spanish horror fans and those just looking for a bit of Eurosleaze. Co-production company Cinevision also produced Tomas Aznar's BEYOND TERROR (also penned by Simon), which would make a neat double bill with SATAN'S BLOOD.