Santo in Black Gold aka Santo en Oro negro opens from a secret base located inside a Puerto Rican prison. Orders go out by radio to New York City to begin “Operación Oro Negro.”
Meanwhile, in New York, a man forces his way into the board room of a large corporation, headed by Vanessa del Valle. The intruder says he represents a terrorist organization run by Acuario, and unless the corporation pays a “tax” on every barrel of oil they produce, their oil installations will be sabotaged. When the police try to seize the man, he leaps out of a window, plummeting to his death, many floors below. Except, he wasn’t human–his shattered corpse contains various wires and transistors instead of blood and guts. Two members of the board of directors go to Mexico and ask Santo for help. They promise to pay him a royalty on each barrel of oil they produce, if he will help them. The money will help feed hungry children in the world. Santo agrees. But first, he wrestles Rebelde Rojo.
In New York, Enrique Artigas visits Vanessa. He is an old friend of her late father, and has helped manage her fortune. But now he wants some romantic payback, and Vanessa isn’t interested. Suddenly several men break in, slug Artigas, and kidnap Vanessa. A few moments later, she reappears, having eluded her captors.
In Puerto Rico, Santo lays out a wide selection of life-like rubber masks. Choosing one that resembles Charles Bronson, he goes out to the “El Sombrero” nightclub, where the buxom Marta Cristal sings a number. Later, Santo and Marta stroll along the beach at night. They are assaulted by a group of men; Santo takes care of some, while Marta–stripped to her very scanty underwear–puts some martial arts moves on another. The assailants flee, leaving Santo and Marta in a romantic clinch.
The police assign Octavio to assist Santo on the case. Santo asks him to find the source of a piece of cloth he tore off the clothing of one of the attackers. Meanwhile, Artigas and Vanessa decide to travel to Puerto Rico to see Santo about their case.
Santo, disguised as a priest, goes to the local prison. When he enters one cell, the guard and inmates slug him and carry him through a secret passage to the terrorists’ headquarters in another wing. A white-coated scientist and two terrorists rough him up, demanding information. Santo doesn’t tell them anything, but he says “You aren’t human beings. Who is the brain who controls you? Are you programmed to answer?” Oddly enough, they are. They tell him Acuario has built 200 robots, and that the prison warden is unaware of their hidden facility. A message comes in that Santo is involved in the case. “Where is Santo?” they demand. “Right here!” Santo shouts, breaking his bonds and attacking them. He peels off the priest-face, revealing his silver mask underneath. Santo manages to defeat the robots, then puts a timer on a big pile of explosives, runs for a long time to get outside, and then the terrorists’ headquarters blows up real good. Santo reassures the warden: “No human beings were killed.”
Santo and Puerto Rican wrestling legend Carlos Colón wrestle Rebelde Rojo and another bad guy wrestler, in a Puerto Rican ballpark. Artigas and Vanessa are in the audience. Later, Santo goes to Vanessa’s home, but discovers she is actually a robot herself. The real Vanessa is a prisoner of Acuario, who is Artigas. Marta shows up, wearing a halter top and miniskirt, and battles the robot Vanessa, while Santo takes on some male robots. Marta whacks the Vanessa-robot, Artigas flees. Santo says he figured out Vanessa was a fake because he asked her a question about a painting on the wall, and “electronic vision can’t distinguish between white and red.”
Back at the nightclub, Marta does a song and dance number in a very scanty costume. Santo and Octavio go back to her dressing room: Marta is Santo’s other agent working on the case. She tells them that the prisoner who was Acuario’s contact has escaped; he is apparently an old acquaintance of hers, because he asked her to go away with him on his yacht.
Santo and the others go to the yacht club. Santo frees an old man, who turns out to be Vanessa’s father–he wasn’t dead, Artigas was just keeping him prisoner. After a long running battle and chase, Santo finally corners Artigas: “You’re an electronics genius but you forgot that a revolver only has 6 bullets.” As the film ends, Santo collects his check for charity, bids Vanessa and Marta goodbye, and departs.