Seven-year-old Wen (Kristen Cui) is spending her vacation with her two fathers, Eric (Jonathan Groff) and Andrew (Ben Aldridge), in a secluded cabin nestled in the heart of rural Pennsylvania. With an extraordinary bond to nature, Wen enjoys collecting various grasshoppers, giving each one a name, and meticulously documenting her observations.
One day, a stranger named Leonard (Dave Bautista) approaches Wen, claiming he needs her and her parents’ assistance to avert a global catastrophe. Leonard’s heavily tattooed appearance piques Wen's curiosity, leading to heartfelt conversations about her unique family situation. Wen reveals that she calls her dads by their first names to avoid confusion, and despite being judged by peers at school, she remains proud of her two fathers.
Wen shares a personal story about her past, recounting how she had a cleft lip at birth requiring several surgeries—a testament to her resilience. However, when Leonard ominously suggests tough choices lie ahead, fear prompts her to bolt back into the cabin, alerting her parents and barricading the door. As they brace themselves, Leonard and his three associates begin knocking, each strike intensifying the tension.
Leonard insists they must enter and converse, but Wen feels frightened of the weapons carried by Leonard and his companions. With their phone lines severed, Andrew tries to bluff, claiming he has a firearm in the truck, but Leonard and his associates break in anyway, wielding makeshift weapons and subduing the family.
Despite their claims of non-aggression, Leonard cleans the area while Sabrina (Nikki Amuka-Bird) tends to Eric, who has sustained a concussion during the struggle. Surrounded by chaos, Redmond (Rupert Grint) exhibits overt hostility toward the family. Leonard reveals they’ve been driven by unsettling visions to locate Wen's family, presenting a dire ultimatum: to prevent an impending apocalypse, the family must sacrifice one of their own. If they refuse, Leonard insists they’ll be the last survivors amidst a world of chaos.
> "You must sacrifice one of your own to save the rest of humanity."
As the family resists the demand, the intruders resort to violence, sacrificing Redmond right in front of them, which unleashes catastrophic events—Eric witnesses a blinding light during Redmond’s demise, while news reports flood in with images of looming tsunamis.
Leonard gives the family until sunrise to ponder their next steps. Amidst the turmoil, Andrew suspects that Redmond may be Rory O'Bannon, a man who once attacked him, deepening the tension as Leonard and his group grapple with their own conscience. As the night spirals, Wen attempts to flee only to be caught and returned.
The following day brings more terror as the group sacrifices Adriane (Abby Quinn), letting loose a deadly strain of flu globally. Eric becomes convinced of a divine purpose, believing they are facing the Four Horsemen of the Apocalypse. With time running short, he offers himself as a sacrificial choice for the sake of his family’s future, envisioning a bright life for Andrew and Wen.
In a heart-wrenching moment, Andrew reluctantly pulls the trigger on Eric, shattering their hopes while they find evidence in the visitors' vehicle that corroborate their shocking claims. As the family escapes toward a diner, they watch news coverage indicating that the disasters have subsided, hinting at a possible end to their nightmare—yet the emotional scars linger long after.
