A young Cristina witnesses her mother undergoing a harrowing exorcism. As her mother calls for Cristina, a demon lunges towards her, leaving visible scratches on her arm. Fast forward to the present day, and we find adult Cristina waking up in a secluded hut in Veracruz, Mexico. Javi, a local man, questions her presence in the eerie region known as La Boca. Enigmatic Luz, a Nahua bruja, peers into Cristina's eyes and ominously states, "She has it." In an attempt to cleanse her, Javi makes Cristina drink goat's milk to purify her soul.
Cristina’s cousin Miranda reveals that she discovered Cristina unconscious in La Boca and brought her to Luz and Javi for assistance. Cristina, a journalist from Los Angeles, returned to her roots to investigate the ruins at La Boca; however, she struggles with a heroin addiction, continuing to inject herself with the remaining syringes while chained to her bed. Despite her claims of being unaffected by demons, odd and frightening occurrences lead her to reconsider.
As Luz and Javi perform a traditional exorcism ritual, Cristina remains skeptical, but the evidence around her is hard to ignore: snakes slither into her room, a rooster appears brutally mangled, and candles extinguish, revealing shadows in the corners. During one startling event, Luz seems to pull animal teeth from Cristina's abdomen, but a snake escapes back inside her.
One fateful night, Cristina, in a fit of rage, chokes Javi until he’s unconscious as she grapples with her situation. However, a line of salt at the door prevents her escape. Her belief in the demon named Postehki—a creature described as "the death god of broken things"—shapes as she realizes he has taken hold of her due to her long-standing battle with depression from her time spent in foster care, leading her to drugs. Postehki has drawn her back to her hometown to finish what he started. Determined to rid herself of this malevolent force, she discards her remaining heroin stash.
As Cristina seeks answers about a mysterious boy she often sees, her companions express ignorance about any child in the vicinity. A breakthrough occurs when she discovers the "broken man ritual," detailed in a book gifted to her by Miranda. Through another intense ritual, Luz temporarily restrains a convulsing Cristina. In a dramatic turn, Postehki exposes itself to Luz, who sacrifices her own life to seize its heart, attempting to save Cristina from its clutches. Tragically, the demon finds a new host in Miranda through the scratches Cristina inflicted earlier.
With sheer determination, Cristina paints her face to fully embrace her role as a bruja. Together, they attempt to draw out Postehki, and in a climactic moment, Cristina captures its heart and tosses it to Miranda, who stabs it, igniting a fire that seemingly vanquishes Postehki for good.
Cristina's ordeal is far from over, as her editor Carson arrives, summoned by locals after finding him near La Boca. While his intention is to rescue her, he brings along more heroin, which no longer holds any sway over Cristina. Instead, she realizes the dark truth that he has also been possessed, prompting Cristina to embrace her newfound role as a bruja as she initiates a ritual to save him.
