In December 2022, Dan Forester, a biology teacher and ex-Green Beret portrayed by Chris Pratt, faces disappointment when he fails to secure a position at a prestigious research center. During a Christmas party, while engrossed in the World Cup, he is startled when soldiers from the year 2051 materialize to deliver grave news: humanity's existence hangs by a thread due to an impending war with alien invaders known as the Whitespikes. This cataclysm is destined to commence in November 2048, leading to the annihilation of most of humankind just three years later. In a desperate measure, military forces worldwide are dispatched into the future through a wormhole device called the Jumplink, although less than 30% return alive within a week, resulting in a global draft.
As the draft persists for a year amid a burgeoning anti-war sentiment, hope dwindles for humanity's survival. Dan receives his draft notice and, along with fellow draftees, reports for basic training. He collaborates with another draftee, Charlie played by Sam Richardson, to conclude that the drafted individuals must have already perished before the war began to prevent any paradoxes. The draftees are then sent to a battleground in Miami Beach, though their drop location is tragically incorrect, leading to a high casualty rate. Under the orders of Colonel Muri Forester, played by Yvonne Strahovski, they embark on a mission to rescue lab personnel in danger of extermination. Unfortunately, they discover the personnel are already dead but manage to salvage their research. When Dan contacts command for assistance, he learns that no one will come to their aid, resulting in the loss of many draftees, with Dan, Charlie, and Dorian, a seasoned soldier portrayed by Edwin Hodge, being among the few survivors.
When they regain consciousness, they find themselves in a military encampment located in the Dominican Republic. Dan is called to meet with Colonel Forester, who shocking reveals that she is actually his grown daughter, Muri. She recruits him for a crucial mission to capture a female Whitespike, a more elusive variant than the typically encountered males. After successfully trapping the female, they are besieged by a swarm of male Whitespikes. As they arrange for a rescue, Muri confides in Dan that his future self, disillusioned with life after a job loss, ultimately forsakes his family and meets a fatal car accident in 2030. Subsequently, Dan, Muri, and the captured female Whitespike are transported to a fortified oil rig situated near Port Nelson, home to the Jumplink.
Together, Dan and Muri work tirelessly to develop a toxin capable of exterminating the Whitespikes, just as they begin to breach the base. However, chaos erupts as the Whitespikes launch an attack, and in the ensuing turmoil, the captured female lethal strikes Colonel Forester. In a desperate act, Dan leaps off with her just before he is whisked back to the past alongside the toxin they need to mass-produce. However, upon trying to communicate with the military, he discovers that the Jumplink is nonfunctional, having been destroyed in the earlier chaos. Panic ensues worldwide, indicating the war is doomed.
As Dan teams up with his wife Emmy, played by Betty Gilpin, they deduce that the Whitespikes may not have arrived in 2048 after all, but perhaps long before. With input from Charlie and Martin, a high school student intrigued by volcanoes, they theorize that the Whitespikes might have been present on Earth since the Millennium Eruption in 946, awakening only due to global warming. Fueled by this hypothesis, Dan leads a mission to Russia with Charlie, Dorian, and his estranged father James, portrayed by J.K. Simmons, to uncover the truth. They stumble upon a downed alien ship while exploring Komsomolets Island, sparking a heated debate about informing humanity of the looming threat. Ultimately, they resolve to eliminate it immediately.
Inside the craft, they horrifyingly realize that the Whitespikes are not aliens but rather bio-engineered organisms, potentially intended as a planet-clearing weapon or livestock for another alien civilization. They inject several dormant Whitespikes with their toxin, resulting in the demise of the injected creatures but awakening others, leading to devastating losses for the team. In a poignant moment, Dorian, who is terminally ill with cancer, elects to sacrifice himself by detonating explosives, annihilating almost all of the Whitespikes. Only Dan, James, and Charlie remain alive to pursue the single female that has fled.
Finally at peace with knowing they have thwarted the war, Dan returns with his father to reunite with his wife and daughter, determined to heed Muri's warnings and not repeat the mistakes of the future.
