Jamie Douglas Booth and Maya Hannah John-Kamen are a young couple living in London. When they learn Maya is pregnant, Jamie celebrates with her, but a sudden assault by a gang shatters the moment and leaves them shaken as they piece together what comes next.
Seeking safety and a chance for a fresh start, they move to a rural house in Ireland that they inherit from Jamie's great-aunt Maeve Niamh Cusack after her death. The place seems quiet at first, but the old estate quickly reveals a troubling history beneath its quiet exterior.
They hire the local Whelan family as builders, drawing into a tense dynamic with a clan that includes the formidable patriarch known as Daddy Whelan [Colm Meaney], his older son Eoin Whelan [Kristian Nairn], and his younger son Killian Whelan [Chris Walley]. Aisling, one of the younger children, also roams the house, often slipping away with small stolen items, while the older boy Eoin bears the weight of harsh discipline. The family’s presence casts a shadow over the home as strange warnings begin to surface.
An old friend of Jamie's aunt, Niamh, cautions Maya about a local myth: every night a liver offering should be left at a door in the back garden for the Red Caps who live in the forest. The couple initially treats the tale as superstition, yet the rhythm of the ritual begins to haunt the household.
Maya learns a disturbing piece of Maeve's past—Maeve once lost a child, a daughter who vanished when she was barely two years old, and the girl’s body was never found. An old story suggests the baby vanished as part of a deal with the Red Caps to save the life of the child’s father, who later dies, though Maya wonders if postpartum depression could explain Maeve’s heartbreak.
As days pass, the Whelans’ violence intensifies. The children’s mischief becomes more alarming, while Eoin speaks privately about abuse he endures from his father, and Maya discovers a stone shrine to the Red Caps hidden near the woods. When she tries to retreat back to the house, she encounters Eoin again and offers him comfort, only for him to lash out before being dragged away by the Red Caps.
That night, Jamie confronts Killian and Aisling in the pub about what happened to their brother. Maya is visited by a Red Cap who presents her with a grisly proof—Eoin's head in a plastic bag. The sight confirms that the Red Caps are real, and the couple’s search for answers becomes a fight for survival as the Whelans attack the house, seeking information about Eoin’s disappearance. Maya is caught with Eoin’s head while Jamie distracts Daddy at the front door, forcing Maya to flee into the woods to seek help from the forest’s inhabitants, offering them anything in return.
In response to Maya’s plea, the Red Caps descend on the house to settle the score. They kill the three Whelans as Maya gives birth, and the infant is taken away by the supernatural beings as payment for their aid. Maya follows the procession to the shrine and discovers an elderly woman who she realizes is the lost daughter of Jamie’s aunt Maeve, kept by the Red Caps. Refusing to let them keep the child or take her, Maya kills one Red Cap and crushes the old woman’s skull with her bare hands. The Red Caps halt before her, reverence shifting to awe as Maya is proclaimed the new “Mother Redcap,” bathed in the blood and skull of the dead, and she and her daughter return to the house under Jamie’s horrified gaze.
