A long-period comet is detected on a collision course with Earth, and the world braces for impact. Amid rising fear, the major nuclear powers unleash intercontinental missiles in a desperate bid to shatter the celestial threat, but their efforts fail to stop the disaster—only fragments survive and begin to rain down on the planet, heralding a cascade of catastrophe.
Research scientist David Dmatti Joe Lando is asleep when his co-worker, Mark T.J. Lepage, calls for urgent help. Rushing to the lab, David discovers Mark convulsing and the water supply poisoned by toxins. Before help can arrive, Mark dies, and a meteor shower wrecks the scene, taking the lives of the paramedics and scattering the remains of David’s work. The danger widens as Alison Madison McLaughlin, David’s daughter, also falls ill after drinking the contaminated water. News outlets report that the comet may harbor a deadly pathogen that has tainted Lake Mead, and the government abruptly orders a quarantine. In the scramble, David is separated from his wife Kate Claudia Christian and Alison as authorities seize control of the city.
Driven by a stubborn will to protect his family, David slips away and heads toward the Las Vegas Valley in hopes of locating a colleague working on an antidote. Along the way, he encounters a young woman in distress, Lynn Cooper Harris, whom he revives at a gas station. She hasn’t been spared by the illness either, and she joins him in a bid to survive. As the couple makes their way toward a safer refuge, they witness much of the surrounding landscape collapse under a merciless meteor shower, and they learn that the quarantined population has been moved toward Los Angeles.
In Las Vegas, an experimental antidote emerges, and David secures a dose to help Lynn and, in turn, to aid his mission. The clock is ticking: the largest fragment is projected to slam into Los Angeles, and a frantic evacuation order is issued. Homeland Security pivots into a crisis mode, canceling the evacuation to conserve resources, but a determined team defies the order, continuing efforts to rescue those at risk. A compassionate pastor Celestial invites David and Lynn to shelter for the night in her church, offering a momentary calm before the next wave of danger.
With time running out, David uses the antidote to save a girl he encounters and learns from the girl’s mother about a possible location where his wife and daughter might be found. The two survivors narrowly escape as additional meteorites strike and decimate the church. Tragedy strikes when Lynn succumbs to the illness, though she had safeguarded the antidote for Alison.
Undeterred, David conquers his fear of heights and climbs a perilous cliff to reach Kate and Alison. He administers the antidote, and the trio watches from a safe vantage point as the final fragment crashes into the city, marking the end of the immediate threat and a hopeful, fragile reunion in the aftermath.
