Santo vs. Black Magic aka Santo contra la Magia Negra opens in a voodoo ceremony, presided over by Bellamira (Sasha Montenegro). Another woman, possessed by the spirit of Damballa, sends Bellamira to the “pool of the gods.” There, she sees Santo receiving orders from Interpol: he must go to Haiti and protect Professor Jordán, who has developed an explosive “more powerful than the H-bomb.”
When Santo arrives, he’s met by Interpol agent Jorge, who also happens to be the fiancé of Lorna, Jordán’s daughter. Two scientists who were working with Jordán recently died-the only marks of violence were small scars on their hearts. Jorge’s car has a blowout on the way into town, and he and Santo are attacked by a group of zombies.
At his hotel, Santo plays a tape of instructions which says he must get Jordán’s formula for “our government” and keep the “eastern republic” from stealing it. Later, an intruder climbs down a rope to Santo’s balcony, and puts a snake on the sleeping wrestler’s chest. Santo wakes up, grabs the snake, and tosses it off the balcony.
Bellamira is in league with two foreign agents; she’s angry that Santo survived the death trap, but swears to get him with her magic instead.
Meanwhile, Prof. Jordán tells Santo that he doesn’t want or need any protection. He spent “hundreds of hours” working on his formula and won’t turn it over so easily, even though Santo says millions of people could die. There are secret uranium deposits on Haiti that can be used to make the new explosive. Santo and Jorge go to a nightclub to see a good voodoo priestess named Michelle, but she won’t help them.
Bellamira leads another voodoo ceremony. She sticks a pin in a little Professor Jordán doll, and the scientist drops dead. The coroner says Jordán had a small scar on his heart, but it wasn’t enough to cause death. Bellamira appears at Jordán’s funeral, and is introduced as Lorna’s best friend. She surreptitiously tosses a little blue ring into the grave; she also asks Santo for his autograph.
Bellamira and the spy duo visit the uranium mines, where slaves are being forced to extract the mineral while being whipped by a cruel overseer. That night, Jordán emerges from his coffin, a white-faced zombie, and goes to his house. He tears out a page from his notebook but is surprised by Lorna, who is understandably shocked to see her dead father walking around. She faints; he makes as if to strangle her, but is repelled by the cross around her neck.
Jorge, although he has previously fought zombies with Santo, doesn’t believe Lorna’s story. But Santo and Lorna agree that her father’s grave must be opened, just to check. However, a court order must be obtained. The next day is carnival time; Santo runs into Michelle, who again refuses to help but promises Santo a magic amulet. That night, Santo wrestles the Black Hood; despite Bellamira’s mental commands to the contrary, Santo wins. He heads for the graveyard where Jorge and Lorna are supervising the exhumation, but has to fight his way past the two foreign agents. The coffin is, no surprise, empty.
The former inhabitant of the coffin is turning over his formula to Bellamira. They test it in a small quantity and it blows up real good. In a cruel gesture, Bellamira then sends zombie Jordán back to his house, where Lorna sees him again! This time, he’s really dead and flops over. Lorna, upset, goes to stay with her “friend” Bellamira. However, that night she wakes up and–clad in babydoll pajamas–follows Bellamira into the jungle. She’s caught by two henchmen. Meanwhile, Bellamira is poking a Santo voodoo doll with a pin, causing the wrestler to writhe in pain. Lorna manages to break the doll and save Santo, and for her efforts is put on the menu as the human sacrifice at the next voodoo ceremony.
Santo beats Rebelde Rojo. Michelle finally comes through with the magic amulet; she also fingers Bellamira as the black magic woman. Jorge, Santo and Michelle go to Bellamira’s house, where they battle with the spies. The agents flee, but leave a wounded comrade behind, who gives Jorge the location of the voodoo headquarters. Santo and the others go there, just in time to prevent Bellamira from killing Lorna. Instead, Michelle challenges her rival to the “test of Damballa.” Santo takes Michelle’s place: he and Bellamira stick their hands into a basket containing snakes, and are both bitten. Moments pass, and finally Bellamira succumbs to the poison and drops dead.
As Santo, Jorge, Michelle and Lorna leave, the spies show up again and there is a brief fight. The police arrive, and everything is wrapped up!