Seven-year-old Wen is vacationing with her fathers, Eric and Andrew, at a remote cabin in rural Pennsylvania. While catching grasshoppers, Wen is approached by a stranger named Leonard. Initially friendly, he explains that he needs Wen and her parents’ help to save the world. However, Wen becomes suspicious when three other people appear with makeshift weapons. Wen flees to warn Eric and Andrew, but the visitors break into the cabin and tie them up, with Eric sustaining a concussion attempting to fight them.

Leonard and his companions—Sabrina, Adriane, and Redmond—claim that they have never met before this day and have no intention of harming the family. However, in the past week, they have been driven by visions and an unknown force to find the family. The group foresees an impending apocalypse in which Leonard claims oceans will rise, a pandemic will spread, the sky will fall, and darkness will envelop the earth. The only way to prevent this is for the family to sacrifice one of their own. They are warned that, although they will survive the apocalypse, if they do not make a choice, they will be the last people alive. Eric and Andrew suspect that the intruders are lying and that the attack is motivated by hatred and delusion.

When the family refuses to make a choice, the intruders sacrifice Redmond by covering his head with a cloth and fatally striking him with their weapons. A concussed Eric sees a figure of light as Redmond dies. On television, media reports show devastating megatsunamis, which Leonard declares is the beginning of the apocalypse. Andrew believes he recognizes Redmond as Rory O’Bannon, a man who had been arrested after assaulting Andrew in a bar years prior. Andrew thinks Rory tracked him down for revenge and manipulated the others to go along with his ruse. Leonard, Sabrina, and Adriane question Andrew’s assumption and grapple with their guilt, but still hold onto their visions. They reveal that Redmond’s death has unleashed the first judgment of humanity. The next day, the visitors sacrifice Adriane as the family remains indecisive. The disasters continue as a deadly variation of the flu virus, to which children are particularly vulnerable, spreads across the world.

Andrew insists the disasters are coincidental and that the intruders were anticipating a pre-scheduled news broadcast. Andrew escapes, retrieves his gun from his car, and shoots at Sabrina until she flees. He finds Redmond’s wallet and proves to Leonard that he was Rory. With their tires slashed, Andrew believes the intruders came in a truck nearby and suggests they use it to escape. As Leonard is being held at gunpoint, Sabrina breaks into the house and is fatally shot by Andrew. Leonard decapitates Sabrina, before overpowering Andrew and taking his gun. The broadcast shows spontaneous plane crashes occurring around the world.

Realizing their time is nearly over, Leonard leads the family to the back deck as the sky darkens. Leonard informs them that after his death, they will only have a few minutes to make a decision, before Leonard slits his own throat. Upon his death, lightning causes fires and more planes to crash. Eric now believes the events are real, and that the intruders represent the Four Horsemen of the Apocalypse. Not wanting Wen to grow up in a destroyed world, Eric offers himself as the sacrifice. He reveals that during Redmond’s sacrifice, he saw a vision of an older Andrew and an adult Wen thriving in the future that prevented the apocalypse. Eric feels that their family was chosen to make the sacrifice because their love was so pure. Reluctantly, Andrew shoots and kills Eric before lightning strikes, setting the cabin on fire.

Andrew and Wen find the visitors’ truck with belongings that corroborate their stories. They drive to a crowded diner nearby, where they watch news reports confirming that the disasters have subsided. Returning to the truck, the radio turns on and plays “Boogie Shoes” by KC and the Sunshine Band, coincidentally the song that Eric had played for them on their drive to the cabin. They drive off, returning into the world.