Plot summary

Dr Marco's [Ronald Remy] most beloved Katrina has died. As a vampire, Marco has devised a plan to bring her back from the dead. It requires large amounts of human blood and will eventually necessitate the transplantation of a human heart. Marco has the heart already picked out. He intends to use the heart of Katrina's twin sister Charito. Charito and Katrina [both played by Amalia Fuentes] were separated at birth. Katrina was raised by their mother Marisa [?], while Charito was raised by Elias [Paquito Saludo] and his wife [Mary Walter], who Charito believe to be her real parents. When Elias and his wife are murdered and return as vampires to Charito, she realizes something isn't right. Fortunately, she has her friend Rubin [?] and visitor-lover Victor de la Cruz [Eddie Fernandez] and his two sisters to protect her. She also has "Aunt" Marisa, who has invited Charito to live with her. Unfortunately, Marisa is allied with Marco and, although she later defies him, is charged with keeping Charito at hand until Marco needs her heart. Although the prayers of the priest are able to release Marco and Katrina from their vampirism for a short time, the monstrous evil of Satan repossesses them again. The time has come to transplant Charito's heart into Katrina. Marco summons Charito through his pet bat Basrah (who snarls like a panther). When Mother Marisa defies Marco's power, Marco has Basrah kill her. As Vincent and the cops arrive, Marco and Katrina attempt to flee. Victor, armed with a flare gun, saves Charito, Marco disappears, and the priest lays Katrina to rest.