The film opens with James reciting a profound passage from Henry David Thoreau, declaring his foresight about the impending societal collapse. In response, he has taken his free-spirited wife Lily and their young daughter Hannah to live a secluded, off-grid life. A striking montage follows, showcasing James' college friends as they grapple with the chaos leading up to this catastrophic event. We are introduced to Benji (a radical activist) passionately speaking at a university, his zeal matched by his affection for Ariel, one of his students. Meanwhile, Nick, James' former business partner, and his wife Becky are on their way for an important meeting at James' place. Then there's Laura, a former aide to a U.S. Senator, who has been denied a job at a non-profit due to a scandalous past affair. Lastly, Lev, a brilliant hacker, contemplates ending his life until he discovers a potential link between a virus and the impending disaster.
As a mysterious "Goodbye World" text floods their phones, the friends gather at James and Lily's isolated Mendocino County home, where Benji reveals that nationwide riots are erupting in response to the escalating crisis.
During a trip into town, Laura and James discuss the attacks. Initially, Laura feigns ignorance but eventually admits that Homeland Security contacted her about Lev's suspected connection to the virus. In this devastated landscape, ruthless bikers have taken over the local store, exploiting the panic-stricken community; Laura resorts to flashing her breasts for supplies in desperation before they flee from witnessing a local man being bullied by thugs. Later, two National Guardsmen show up at their homestead, asking to use it as a base. Although they request assistance, Becky challenges their presence on Constitutional grounds, while James politely insists they leave.
As tension builds, Laura decodes a presidential broadcast indicating that the U.S. is under martial law. Old rivalries and unresolved issues resurface among the group, leading to increased friction. Becky's Libertarian beliefs clash with the group's ideals, and a heated argument erupts between James and Nick over an unresolved lawsuit linked to their past business partnership. Amid mounting discord, the friends must confront their differences to survive in this changed world.
As the atmosphere becomes more strained, Benji takes a firm stand, telling Ariel to leave, but James defies him and insists she stay. Ariel's disruptive behavior escalates tensions further, resulting in Lily intervening to support Benji's decision. Meanwhile, the emotional connection between Nick and Lily deepens, prompting Lily to demand a divorce from James, who responds apathetically, focusing on his personal woes rather than the state of his marriage. Ariel's eventual departure leads her to take refuge with James' neighbors, who are—unbeknownst to James—hosting the very Guardsmen he refused to assist.
As Ariel integrates into her new environment, she divulges critical information about James' supplies to the Guardsmen, catching their attention. Damon, one of the more intimidating Guardsmen, demands James hand over all his provisions, a request James adamantly rebuffs. When Damon resorts to threats against Laura and Lev, James reluctantly agrees to deliver supplies the next day to avert violence.
Lev then reveals a startling detail: he had been contracted to create a virus capable of incapacitating an entire nation's technological framework. Fascinated by the challenge, he ultimately released a devastating virus into the digital world, triggering the collapse of societal infrastructure.
In the ensuing mayhem, Becky discovers Benji ensnared in a bear trap. After assisting him, they bond over their joint predicaments, leading Benji to confide in her about Nick and Lily's growing relationship. Becky confronts them after Nick and Lily briefly leave together, only to return as Lily persuades Nick that their friendship is more important than romantic interests.
James visits his neighbors to strengthen ties, adamant about not relinquishing his supplies despite naive requests for help. Just as Damon prepares to retaliate against James, Laura intervenes, neutralizing the threat and claiming half of the Guardsmen’s medical stock for their group. She underscores the necessity of unity for their survival.
In the aftermath of the turmoil, Nick returns home, leading to a reconciliation between James and Lily. Laura forms a new connection with Lev, while Becky and Benji set out to continue their humanitarian efforts. The remaining five friends, two of whom played significant roles in the demise of modern infrastructure, are later seen cultivating gardens with fellow survivors, symbolizing hope and resilience amidst chaos.
