Santo at the Border of Terror aka Santo en la frontera del terror aka Santo vs. the White Shadow begins with Gerardo and Fernando making arrangements to cross illegally from Mexico to the United States. The “coyote” who will take them across says they’ll work on Mr. Richards’ ranch, and will be well-paid and well-treated.
Fernando wants to earn money to pay for an operation for Florecita, the little blind sister of his girlfriend Azucena, who sings in a cantina. When Fernando and Azucena are attacked by some drunk customers, Santo and his sidekick Carlitos, who were passing by, help out. Santo takes off his mask so Florecita can feel his face. He says he’ll pay for her operation. Fernando and Gerardo are still going to the U.S. to work; Santo says he’ll be wrestling in gringo-land so they can look him up if they need help.
Gerardo and Fernando cross over and are hired by Mr. Richards. His foreman Monk is a surly looking character, and a mysterious looking Dr. Sombra gives each new man a physical examination. Later, he calls a contact in McAllen, and says “the merchandise has arrived.” Dr. Sombra and his armed guards take one of the farm workers to his operating room. The next time he’s seen, Sombra has some eyes in a glass jar! The dead “donor” is taken away to be buried. Sombra will use the money he gets selling the stolen eyes to finance his brain transplant experiments. He has two zombie-like assistants, the results of some earlier surgical hijinks. Monk is eavesdropping and decides to cut himself in on the action.
Meanwhile, Azucena is worried since Fernando hasn’t contacted her. Santo and Carlitos arrive at the ranch; Santo sneaks in. Meanwhile, Monk tries to blackmail Dr. Sombra but is locked up, along with Gerardo and Fernando who were caught trying to escape. Dr. Sombra says the Mexican workers died to save the lives of those “more worthy than they were.”
Santo breaks in and questions Sombra. He frees Gerardo, Fernando and Monk. However, Sombra and his zombies eventually capture Santo. Monk is shot in a struggle. Sombra hypnotizes one Mexican and sends him back to Mexico to lure new workers to the ranch with tales of high salaries and good treatment. Sombra and his zombies put Santo and Carlitos in a cabin with a time bomb.
Meanwhile, ranch owner Mr. Richards has returned and freed Gerardo and Fernando. When a helicopter lands to pick up the jar of eyeballs, the jar is missing: Richards has it. He was investigating Sombra’s past, and a shady past it was, too. Sombra sends his zombies to grab Richards, Gerardo, and Fernando. Santo and Carlitos intervene, so Sombra tries to make his escape via helicopter, but Gerardo grabs a gun and shoots it down.
Back in Mexico, Santo, Gerardo, Fernando, Carlitos and Azucena are present when Florecita’s bandages are removed: she can see!