After years devoted to caring for her terminally ill mother, who has recently passed away, Ambar Cruz embarks on a new chapter as an undocumented immigrant in Ohio. Seeking stability, she rents a room in a boarding house managed by Red and his obscure brother Becker. However, Ambar's transition into this new life is plagued by unsettling visions of women who seem to haunt the house, alongside terrifying nightmares involving an unseen entity linked to an ancient stone box.
As the days pass, Ambar encounters other resident immigrant women, including Freja, Petra, and Maria, adding to her sense of isolation and confusion. One day, while Red is preoccupied, Ambar dares to explore a forbidden study. There, she uncovers disturbing artifacts, audio tapes, and files that were amassed in Mexico by Red and Becker's parents, Professor Arthur Welles and Mary. These documents reveal Mesoamerican rituals centered on human sacrifices and suggest a connection to the stone box that haunts Ambar's sleep.
Things take a darker turn when Ambar's coworker Kinsi swindles her out of cash with phony promises of fake identification, only to vanish shortly after. To compound her woes, Ambar loses her under-the-table factory job due to a misunderstanding with her boss. When supernatural occurrences begin to infiltrate Ambar's room, including anguished cries echoing from the shower drain and disturbing apparitions like Freja, her anxiety heightens. Despite her attempts to reach out to family friend Beto for help, he dismisses her plea, leaving Ambar feeling trapped.
Determined to reclaim her security deposit, Ambar arranges a meeting with Red at a diner. Yet, when he arrives without the money, he manipulates her into returning to the boarding house. Back in her room, Red reveals his family's dark history, including how his father was a man obsessed with collecting bizarre artifacts and committing heinous acts. He claims that his mother became a victim of these twisted rituals, and as he speaks, a sinister presence looms.
With fear mounting, Ambar learns from Petra and Maria that they seek her assistance in escaping Becker. During their desperate conversations, they discover a shared dream about the ominous stone box, which Petra suspects might be hidden in the basement. Tension escalates when the brothers attempt to collect the three women, only to be interrupted by Beto looking for Ambar. In a shocking turn, Becker brutally murders Beto.
Red discloses the horrifying truth of their past; his father coerced his mother into helping him murder women as part of a bizarre ritual he claimed could cure ailments. After killing their father, both brothers were left haunted, but Becker became fixated on the belief that the stone box could heal him as well. Ambar becomes increasingly desperate, pleading for her life, but Red is insistent on aiding his brother's twisted goals.
In a chilling climax, Becker chains Ambar to an altar in the basement, leaving her alone with the stone box, from which a creature emerges. The entity brings Ambar visions intertwined with her past—seeing herself embracing her dying mother while in reality, the beast begins its grisly work. Just as all hope seems lost, Ambar resists, taking drastic action to push the creature back into the box by confronting the truth of her mother's dying memories.
After a fierce struggle in which Ambar retrieves a ceremonial weapon from the forbidden study, she fights back against both brothers. However, tragedy strikes as Petra sacrifices herself to save Ambar but is irrevocably lost when Becker casts her to her death down a stairwell. Fueled by anger and desperation, Ambar ultimately defends herself against Becker, ending his life in a brutal clash.
However, her vengeance does not come without cost; she drags Red to the altar, where he, too, meets a grisly fate at the hands of the creature, joining the realm of the ghosts trapped within the house. Wounded but determined, Ambar stumbles toward the exit, feeling an unsettling transformation within her as her injuries inexplicably heal. Yet, the dangerous legacy of the box stirs within her, threatening to claim her as it did Becker before.
