Certain Dark Things

In an alternate Mexico City where vampires are a known species banned from the city for 30 years, 17-year-old Domingo scrapes by as a garbage collector, sleeping in abandoned tunnels beneath downtown. One night in the subway, he follows a striking young woman with a genetically modified Doberman onto a train. The woman, Atl, invites him to her apartment and reveals she is a Tlāhuihpochtli, a subspecies of vampire native to Mexico with roots tracing back to the Aztecs. She offers Domingo money for his blood, explaining that her subspecies feeds only on the young. He agrees, and during the feeding, her hair turns to feathers and her hands become talon-like.

Atl is a 23-year-old fugitive, the second daughter of Centehua, leader of the Iztac clan, a powerful vampire narco family in the northern state of Sinaloa. After a rival Necros (a European vampire subspecies) narco lord named Godoy murdered their mother, Atl's older sister, Izel, chose not to retaliate. Atl defied her, killing two of Godoy's nephews and his pregnant concubine. Godoy's forces retaliated by storming the compound with flamethrowers, burning Izel alive and massacring the clan. Atl survived by hiding in a refrigerator and fled south with her dog, Cualli. She now seeks Verónica Montealban, her mother's former tlapalēhuiāni (trusted human companion), hoping Verónica can provide forged documents for an escape to Guatemala.

Meanwhile, Rodrigo, an experienced human operative serving the elder Godoy, arrives in Mexico City with Godoy's reckless 21-year-old son, Nick. Their mission is to capture Atl. Nick, a Necros vampire who can enslave humans through blood contact, sneaks out to a nightclub and kills a young woman. The case falls to Detective Ana Aguirre, a middle-aged investigator who transferred from the state of Zacatecas to escape vampire violence. Ana traces the killing to the Godoy family. Her investigation draws the attention of Deep Crimson, a powerful human gang that helped expel vampires from Mexico City in 1992. Deep Crimson's leader, Valentina Saade, hires Ana as a consultant for her expertise in hunting vampires.

Domingo returns to Atl's apartment and offers himself as a steady blood source. Atl performs a reciprocal blood-bonding ritual, creating a xiuhtlahtōlli: a telepathic bond that allows them to share memories. She sends Domingo to visit Bernardino, an elderly Revenant vampire in the Roma neighborhood. Revenants are feared because they can drain life force from any living creature. Bernardino reluctantly provides a lead to Verónica, who now lives under the name Elisa Carrera. Atl manipulates Elisa into producing fake passports and arranges to collect them at the Tenampa bar in Plaza Garibaldi.

As Atl's hunger intensifies, triggering her species' compulsion to count small objects, armed attackers ambush them outside her apartment with silver nitrate darts. Atl kills several but takes three darts, triggering a severe reaction. Domingo drags her to his underground tunnels. Desperate, he bribes an acquaintance with some veterinary training to treat her at the Jackal's dog-fighting kennels. The Jackal, a local gang leader, locks them in a cage, planning to sell Atl for the bounty on her head. Atl recovers enough to stage a violent breakout. During the escape, she feeds from Belén, Domingo's former girlfriend, until Domingo forces her to stop at gunpoint. Nick and Rodrigo arrive shortly after. In a brutal confrontation, Atl shoots part of Nick's jaw off but is badly beaten, and they barely flee.

They take refuge at Bernardino's house. Bernardino diagnoses that Nick's bite has infected Atl's hand with a lethal disease unique to Necros biology and amputates it, then transfers life energy to her through his Revenant ability, saving her life. He assures them the hand will regenerate. During Atl's recovery, Bernardino warns Domingo privately that vampires are defined by their hunger and that Atl would kill him if forced to choose between her survival and his. Domingo refuses to accept this. That night, he and Atl share their first kiss, and she confesses to having killed people. He stays, and they spend the night together, Atl revealing the massive, shimmering black-blue feathered wings she can sprout from her back.

At the Tenampa bar, Elisa provides forged documents but refuses to drive them out of the city due to heightened police checkpoints. Domingo proposes walking through Bordo Blanco, a massive landfill on the city's edge that he knows from years of garbage collecting. Bernardino provides a contact, Manuel Tejera, a former smuggler who agrees to drive them to Guatemala from outside the city.

Before they can escape, Rodrigo and Nick ambush Ana outside her apartment, threatening her daughter, Marisol. Nick bites Ana and places her under his mental control. Under compulsion, Ana reveals Atl's location and phones Deep Crimson to trigger a raid on Bernardino's house, a move Rodrigo intends to exploit. During the raid, Nick's command compels Ana to shoot her own allies. Bernardino knocks Ana unconscious, breaking Nick's hold, and despite being shot with silver bullets, helps Atl escape toward Bordo Blanco. Nick reestablishes control over the injured Ana and learns their destination.

The final confrontation unfolds in the vast, dark landfill. Bernardino kills Rodrigo by draining his life force but is impaled by Nick on a piece of rusty metal. Nick threatens to kill Domingo unless Atl surrenders. She hears Domingo scream and turns back. Together they fight Nick: Domingo stabs him, and Atl drives the knife into his eye. Ana, whose connection to Nick breaks momentarily, shoots him in the chest of her own volition. Nick forces Ana to turn the gun on herself, killing her, but her shot creates an opening. Bernardino, still alive, seizes Nick and drains him completely, reducing the young Necros to a shriveled carcass. He then transfers more life energy to Atl, healing her at the cost of his own vitality.

At the road outside the landfill, Atl hands Domingo a backpack with cash and fake IDs and tells him she is leaving him behind. She insists he would slow her down and delivers a final, cutting line: that vampires always lie. He tells her he loves her. She cups his face, kisses him briefly, and walks to the waiting car. Domingo discovers Cualli survived a gunshot wound and carries the injured dog away in a shopping cart. Days later, through their blood bond, he dreams of Atl hacking through a jungle with a machete, her hand fully regenerated. She pauses as if hearing someone call her name, smiles, and presses deeper into the greenery. In his dream, Domingo smiles too.