In 1673 Mexico, a joyful family spends time together in a sunny field, where the youngest son gifts his mother a cherished necklace. However, a dark turn of events ensues when he stumbles upon his mother in a horrific scene, drowning his brother in a stream. Traumatized, he flees, only for his mother to catch him; tragically, he is presumed drowned as well.
Fast forward to 1973 Los Angeles, where caseworker Anna investigates the truancy of her client, Patricia Alvarez, and her two children. Upon arriving at Patricia's home for a welfare check, Anna finds the children locked away, despite their pleas for her to leave them there. Ignoring their warnings, she confronts Patricia, leading to a violent altercation that results in Patricia's arrest. The boys, Carlos and Tomas, urgently advise Anna to keep them safe, but her actions instead put them in grave danger at a child-services shelter. There, amidst a disturbing atmosphere, Tomas sleepwalks, which leads both boys to encounter a ghostly woman in white who terrorizes them.
Tragedy strikes again when the boys are later discovered drowned in a river, prompting Anna’s return to the scene. She brings along her own children, Chris and Sam, who wait in the car while Anna investigates. In a chilling twist, Patricia, accused of the murders, screams accusations at Anna, blaming her for the deaths of her children while revealing that she prayed to the malevolent spirit of "La Llorona" to take Anna's children in exchange for her own.
Chris's curiosity leads him away from the car, and he becomes another target of La Llorona (The Weeping Woman), suffering burns on his wrist from her grasp. The next day, Sam similarly encounters La Llorona, resulting in identical burn marks. Anna's inquiries reveal Patricia has an alibi, yet Patricia harbors deep resentment towards Anna, seeking revenge through dark means.
In a desperate plea for help, Anna seeks guidance from Father Perez, who connects their ordeal to a haunted porcelain doll he once encountered. He instructs Anna to seek out former priest Rafael Olvera, who is now a folk shaman and may possess the knowledge to combat the malevolent spirit. Upon his arrival at Anna's home, Rafael sets up protective items. That night, La Llorona launches relentless attacks, attempting to drown Anna and Sam in their pool.
During the chaos, Patricia returns, armed and intent on delivering Anna's children to La Llorona. However, torn by the realization of her own painful loss, Patricia ultimately helps Anna regain control of the situation, allowing Anna to protect her children. Chris distracts La Llorona by revealing the necklace she had once given to her son, causing a momentary shift in her appearance as she longs for him. In a frantic moment, however, Sam inadvertently unveils a mirror, snapping La Llorona back to her terrifying form.
In a climactic confrontation, Anna drives a cross made from the sacred Fire Tree—witness to La Llorona’s notorious crime—through her chest, vanquishing the spirit once and for all.
With the danger finally passed, Anna and her children express their gratitude to Rafael for his pivotal role in their survival. As he departs, Anna gazes into a puddle nearby, signaling the end of their harrowing journey.
