Ulises, Gustavo Sánchez Parra, grows frustrated as he sits in a bus depot during a massive storm while his wife gives birth nearby in Mexico City. The air is thick with dread as intermittent radio updates from Fernando Becerril reporting worsening news hint that the storm could be a worldwide phenomenon of unknown origin. Ulises tries to call the hospital through the station’s payphone, but the line keeps disconnecting. He then asks to use the elderly clerk Martin’s phone, only to learn there is no outside line.
Irene, Cassandra Ciangherotti, a pregnant woman, seeks shelter at the depot. Ulises suggests she try calling a taxi with the payphone, and when she says the taxi is on the way, the miner offers to split the fare. Irene goes to the restroom, where Rosa, Catalina Salas, a cleaning woman, insists she stay. Irene attempts to flee Rosa, but Rosa suffers a seizure.
Three more people arrive: Alvaro, Humberto Busto, Gertrudis, Carmen Beato, and Gertrudis’s son Ignacio, Santiago Torres. Hearing Irene’s cries for help, the group steps in to assist. Martin, his face bandaged, emerges from his office with a rifle and blames everything on Ulises. Ulises protests that he’s just a miner worried about his wife.
An older woman, Roberta, María Elena Olivares, also suffers an epileptic seizure identical to Rosa’s. The group disarms and ties up Martin. Alvaro grows cautious when he sees Gertrudis inject Ignacio with a hypodermic needle, and he recognizes Ignacio as a famous unsolved medical case. Then Martin reveals that his own face has morphed to resemble Ulises.
Roberta’s features begin to mirror Ulises’s, with facial hair appearing on her skin as the transformation spreads. Irene also undergoes a startling change. Alvaro tries to leave, only to find the doors locked and bulletproof.
Alvaro and Irene inspect Martin’s office and discover that photographs, statues, and posters now bear Ulises’s face. Ignacio locks Gertrudis and Martin in a back room, where Rosa has transformed and has killed herself. Ignacio shows Ulises a comic book about aliens who steal humanity’s individuality. After all have transformed, humanity’s memory is wiped, and people once again perceive themselves as individuals—unaware they have collectively lost their identity. When Gertrudis escapes, she explains that Ignacio has caused the comic book to come true.
Ignacio reveals he was preventing their departure. When the others confront him, Ignacio uses his reality-altering power to stop them. As Ulises dies, he claims not to recognize the others’ faces. In Ulises’s wallet, a picture of the original Ulises—unbearded and unlike the cloned version everyone now bears—tips the group that Ulises was the first to transform. Irene dies during childbirth, and her baby bears the cloned face. Ignacio collapses, and Roberta concludes he made contact with the aliens and, doubting their reality, allowed them to control him.
Police arrive and arrest Alvaro, blaming him for the deaths. Gertrudis and Ignacio head toward Tlatelolco, Mexico City. A final narration notes that, with few exceptions, Ignacio is the only one to remember what happened, much like the comic book.
