Following the tragic and seemingly suicidal death of her husband, James, Harper Marlowe decides to take a much-needed break in the serene village of Cotson, Herefordshire. Memories reveal that Harper had long been weary of James's emotional torment, leading her to contemplate divorce. As tensions escalated, James made desperate threats of self-harm, culminating in an incident where he struck Harper in anger. Following this confrontation, she locked him out, only to witness his fatal plunge from their balcony, a gruesome fall leaving him partially impaled.
Upon her arrival at the quaint country house she has rented, Harper is welcomed by the house's quirky yet well-intentioned owner, Geoffrey, who enthusiastically shows her around the property. Venturing into the nearby woods, Harper discovers an old railway tunnel, where she is suddenly startled by a distant figure screaming and rushing towards her. Panicking, she retreats through the forest to an open field, only to catch sight of a naked man staring at her from afar, adding to her sense of unease.
The following day, during a video call with her friend Riley, Harper is horrified to spot the same naked man lurking in her front garden, his visage marred with blood. In a panic, she locks the door, but the man inexplicably thrusts his hand through the letterbox. Terrified, Harper contacts the police, and the man is apprehended, only for her to realize that one of the arresting officers bears an uncanny resemblance to Geoffrey.
Seeking solace, Harper visits a local church, where she encounters carvings of the Green Man and Sheela na gig. There, she meets a young boy and a vicar who both eerily resemble Geoffrey. In a confounding conversation, the vicar suggests that Harper might share some blame for James’s death due to her refusal to let him apologize, prompting her to storm out. Later, at a nearby pub, she runs into Geoffrey again, where she notices that the few patrons and even the bartender all mirror his appearance. Her agitation spikes upon learning from a policeman that the naked man has been released, as no legal grounds exist to hold him.
In a bid to feel safe, Harper reaches out to Riley, who promises to drive over the next day to support her through the remainder of her vacation. However, attempts to share her location are thwarted by persistent phone service disruptions. The situation spirals when she spots the policeman outside, only for him to vanish as the lights flicker ominously. A male patron from the pub then aggressively pursues her, forcing Harper to retreat to the safety of her house. She prepares to defend herself by arming herself with a knife just as a window shatters in the kitchen. Geoffrey arrives, explaining that the broken window was an accident caused by a crow, which he promptly euthanizes.
The atmosphere grows increasingly sinister when the lights flicker again, and the naked man reappears, compelling Harper to flee back inside as he lunges toward her. In the chaos, he grabs her hand through the letterbox, resulting in a violent struggle in which she stabs him. In a horrific twist of fate, the injury he sustains mirrors the one James suffered from his fall. Soon after, the boy and the vicar appear within the house, both bearing similar wounds. When the vicar attempts to attack her, Harper defends herself, stabbing him before managing to escape.
In a desperate bid for freedom, Harper attempts to flee in her vehicle but inadvertently runs into Geoffrey, who savagely drags her from the car before commandeering it for a chaotic chase, ultimately crashing into a stone wall. As she regains her composure, the naked man reemerges, now transformed into the full embodiment of the Green Man, sharing a grotesque bond with the injuries sustained by James. In an unbelievable sequence, this nightmarish figure gives birth to the boy, who then births the vicar, followed by Geoffrey, and ultimately James—all in a grisly display of violence and death.
In a haunting moment, Harper finds herself sitting next to James in the house, and when she inquires about his desires, he chillingly replies that all he wants is her love. The next day, Riley, who is revealed to be pregnant, arrives, trailing a blood-stained path leading her to Harper, who offers a strange smile upon their reunion.
