In the year 1536, an alchemist in Veracruz develops a mechanism that can give eternal life. In 1937, an old building collapses and the alchemist, who has marble-white skin, is killed when his heart is pierced by the debris. Investigators go to search the home of the alchemist, but they never reveal what else was discovered in the home: Basins filled with blood from a corpse.
In 1996, an elderly antique dealer, Jesús Gris, notices that the base of an archangel statue is hollow. He opens it and finds the 460-year-old mechanism. After he winds the ornate, scarab-shaped device, it unfurls spider-like legs which grip him tightly and inserts a needle into his skin, injecting him with an unidentified solution. An insect — entombed within the device and meshed with the internal clockwork — produces the solution. Gris eventually discovers his health and vigor are returning, as is his youth. His skin loses its wrinkles, his hair thickens and his sexual appetite increases. He also develops a thirst for blood. This initially disgusts him, but he eventually succumbs to the temptation. He uses the device later that night but says his nightly prayer as he does. His granddaughter Aurora notices this and begins to worry about Gris.
Meanwhile, a rich, dying businessman, Dieter de la Guardia, who has been amassing information about the mechanism for many years, has been searching for the statue with the device. He sends his thuggish American nephew Angel, who suffers his uncle's abuse on a daily basis for an inheritance, to purchase the statue at the antique shop.
During a New Year's Eve party, Gris sees a man bleeding from the nose and follows him into the men's room in order to take his blood off of the sink countertop. Another man comes out of one of the stalls, sees the blood and cleans it up. Gris notices blood on the floor and decides to lick it up, until an unknown man walks up and kicks him in the face, knocking him unconscious. He is found by Angel, who gives him some alcohol and tries to beat him into giving up the mechanism. When Gris faints, Angel places his body inside a car and pushes it off a cliff. Gris briefly awakens and prays for survival, but seemingly dies. He later revives in an undertaker's establishment and escapes before he can be cremated. He returns home, and Aurora lets him in. Dieter beats Angel for not ensuring Gris's heart was destroyed and sends him to check on the body. Gris works on a letter to his wife in which he comments on the changes to his body and tells her that after completing some 'unfinished business' he will return to her. He notices that his skin burns in the presence of sunlight and sleeps in a box to avoid it.
Eventually, Gris and Aurora bring the mechanism to Dieter's headquarters, where the businessman offers him a "way out" in exchange for the device. Gris comments on his damaged skin and the businessman tells him to peel it off because he has new skin underneath, which is marble-white like the dead alchemist. Gris threatens to destroy the mechanism but is told that he will die should that happen. Gris agrees to hand it over in exchange for knowing the "way out", whereupon Dieter stabs him. Before being able to strike the killing blow to the chest, Dieter is incapacitated by Aurora and Gris feeds on Dieter. Angel finds the dying Dieter and crushes his throat with his foot, tired of his abuse and waiting for his inheritance. Angel confronts Gris on the rooftop of the building and beats him severely. Gris throws them both off the roof, killing Angel.
Aurora finds Gris unconscious and uses the mechanism to wake him. Noticing that her hand is bleeding, Gris is tempted to feed off his granddaughter but he eventually controls himself. He then painfully destroys the mechanism, despite previous warnings. He returns to his home and is shown lying in bed, with Aurora and his wife in attendance, as the film ends.
