As Pastor Dan settles into his new life as the spiritual leader of Stull, Kansas, his family—including his wife Wendy and their three children, Rebecca, Mary, and Christopher—begin to get to know their small-town environment. Their unsettling introduction to the community begins when Rebecca spots a teenage boy named Noah committing a gruesome act by slaughtering a sheep and collecting its blood. This disconcerting moment is quickly followed by Dan's encounter with the town's friendly farmer, Mason, and the warm greetings they receive from Pastor Kingsman, the former pastor, along with other townsfolk.
As the night deepens, Rebecca is plagued by a haunting nightmare that hints at the disturbing events to come. The following day, they receive a cake from a parishioner, a gesture to welcome Dan into his new position. However, the cake has a strange surprise, as Mary chokes on a tooth hidden within. This unsettling twist is intensified when Rebecca meets Noah once more, and he takes her on a whirlwind tour of the town, before being abruptly summoned by Mason at Pastor Kingsman's request.
Returning home, Rebecca finds Mary is feeling unwell, while Noah receives troubling orders from Pastor Kingsman about carrying out divine duties. It becomes evident that Mary’s unsettling discovery of the tooth has marked her as "the chosen one," in accordance with an old tradition indicating that the first to find it is predestined for something significant.
As the Summer Festival approaches, Wendy and her family dive into preparations for the celebration. The children explore the town, where Rebecca reconnects with Noah, leading to a sweet date atop a fire lookout tower, surrounded by nature's serene beauty. It is here that Rebecca notices a scar on Noah's hand, which he attempts to hide. Just as they indulge in the picturesque view, an ominous figure watching from below disrupts their blissful moment, casting a shadow over their evening.
The next day at the lively festival, Noah whiskers Mary and Rebecca away to a lemonade stand. Unfortunately, their innocent outing is upended when Mary’s drink is unexpectedly tainted with poison. As her condition worsens, she struggles to return home, only to be kidnapped by the malevolent Mason. Bound and vulnerable, Mary learns from Pastor Kingsman that she has been selected according to a dark divine will, as the pastor releases a portal that allows the Devil to seize her spirit. Under the guise of concern, he returns her to her family, feigning normalcy.
Meanwhile, Noah grapples with the weight of revealing Mary's fate to Rebecca, but is interrupted by Christopher's timely appearance. The situation spirals out of control as Dan arrives at the church, responding to a summons from Pastor Kingsman. It’s a grave mistake; he is drugged and imprisoned, rendering him powerless against the pastor's evil machinations. Back at home, Mary awakens unmanned by darkness, regurgitating a foul substance that sends her family into chaos. In haste, Wendy sends the other children off to find Dan. With Noah's help, they break into the church, only to find Dan unconscious on the floor, and a feeling of dread envelops them as they rush him back home.
Upon their return, the family is struck by an eerie scene: every house in the neighborhood is marked with a blood-like 'X' on the doors, a chilling sight that terrifies Rebecca. As she presses Noah for explanation, he remains tight-lipped. Approaching their own home, a nightmarish revelation awaits: Wendy lies lifeless and decomposing on the couch. Dan stumbles in, overwhelmed by horror as Mary, possessed, creeps down the stairs toward him. In a frantic effort to evade the unfolding doom, Dan commands Rebecca and Noah to escape, leaving behind the hope of saving their family.
As he remains in turmoil, Dan tries to save Mary, who eerily mirrors Wendy’s tragic fate in the front yard. Meanwhile, Rebecca's anxiety drives her to take control of the car, clashing with Noah as they navigate the unfolding chaos. Unbeknownst to them, Christopher watches in fear as Mary emerges from the shadows, her presence spellbinding and foreboding.
In a shocking twist, Noah takes Rebecca back to the car and sprints away, abandoning Christopher to the dark fate that awaits him. Just as Christopher finds refuge in a neighboring home, Mary seizes her chance to infect him with her dark malevolence. His desperate cries go unheard as the fear-ridden patriarch ejects him, only for Noah to thwart her attempt at claiming more victims.
Noah then takes drastic action, pushing Rebecca back toward the car before fleeing himself, leaving Christopher to fend for his life. The vehicle's engine coughs to a halt, as Mary approaches, leaving all hope dwindling. Just when things seem dire, Rebecca returns, only to face the horrifying reality: Mary has taken Christopher as her own.
The climax of despair leads Noah to an abandoned church gathering, with Rebecca soon following, bringing tension to a peak. In a moment of reckoning, Noah cuts open Mary’s wrist, using her blood to banish the Devil, sealing the horrifying portal for good.
As Rebecca lies in a trance, radiant with a strange light, the townsfolk gather around in a blend of awe and fear. Following this harrowing experience, a new family arrives, introducing a young boy who will soon inherit Noah's legacy through a disturbing sheep sacrifice, continuing the cycle of grotesque rituals.
