Four couples come together for their usual brunch, but what was once a cheerful gathering has become a tense and awkward affair. Among the group is Glenn, who is introduced to the others for the first time as he’s on his third date with the notoriously discerning Dr. Tracey, played by America Ferrera. As the brunch unfolds, they await the notoriously late fifth couple, Jenny and Gordon. The gathering soon turns into a chance to reconnect with old friends and learn more about the new guy in their midst. When the men briefly excuse themselves to catch a football game, they find themselves cut off from the outside world: the TV, Internet, and landline phones have all gone down. This leads to increasing tensions as host Pete confronts his wife, Emma, revealing their impending divorce to their unsuspecting guests.
Things take a bizarre turn when their neighbor Hal shows up in a hazardous materials suit, delivering the bombshell news of multiple dirty bombs going off in major U.S. cities, including one alarmingly close—just 12 miles away. Faced with the possibility of disaster, the couples hurriedly split up to gather emergency supplies and secure the house with duct tape. During this frantic search, shocking secrets come to light, including affairs among the couples and advances made towards Glenn by the swinging couple, Buck and Lexi, whom he quickly rebuffs.
The anxiety escalates as they hear through a shower radio that the bombs contained the deadly VX nerve agent. Hedy, the chemistry teacher in the group, comprehends that the chemical nature of the attacks leaves them with mere hours to live. After initially slipping into a state of shock, she suddenly requests Scotch. Later, Hedy concocts a batch of "poor man's ecstasy" from various medications she scavenges, leading to a moment of clarity that prompts her to break off her six-year engagement to Shane, further energizing her to lead a musical session, or "dance party," in the living room with Lexi and Buck.
Shane resorts to survival tactics he learned from comic books and classic zombie films like Night of the Living Dead, becoming increasingly paranoid about outsiders, including Glenn. His demeanor grows suspicious, leading him to make others on guard for signs of mutation. He even questions Dr. Tracey about how quickly such mutations could manifest, despite her obvious frustration with his misconceptions. Their interactions are tense as she eventually concludes they shouldn't let the fifth couple into their home when they finally arrive, primarily due to their being habitually late and past conflicts between the women over a man from a previous New Year’s celebration.
In a moment of desperation, Shane decides it’s best to abandon the house for the outside world. He proposes that they drive to seek out other survivors or meet their fate, but to their dismay, the SUV’s battery is dead from playing satellite radio too long. Faced with these compounding challenges, the group reluctantly decides to stick together and enjoy the meal they had planned, making the best of what time they have left.
In an unexpected twist, Glenn ventures into the cellar to fetch wine, only to be caught by Tracey as he adds rat poison, sleeping pills, and muscle relaxants to the mix. He explains that he believes they’re facing The Last Judgment and wants to spare his non-believing friends from the horror of the Great Tribulation. When Tracey relays this revelation upstairs, the others are skeptical of Glenn's mental state but remain unconvinced by her concerns. They conduct a tense discussion about their impending demise, and surprisingly, Hedy acknowledges that a swift death would indeed be simpler than succumbing to the agonizing affects of VX.
Eventually, they collectively decide to drink the poisoned wine. After several counts where everyone in the group pretends to partake, including Glenn, who anticipated their hesitance, they prepare for a final collective toast. As they count down and drink, their fate hangs uncertain in the chilling air of that fateful afternoon.
