John Garrity, a structural engineer living in Atlanta, receives an emergency presidential alert on his phone, announcing that he and his family have been selected for emergency sheltering as a massive comet named Clarke is on a collision course with Earth. With the comet's fragments causing vast destruction globally, John, his estranged wife Allison, and their diabetic son Nathan must navigate the chaos to reach the military planes designated to transport them to a safe location. As the initial fragment strike wreaks havoc, society begins to break down, leading to overcrowded highways and increasing desperation among people trying to survive.

With time running short and societal order collapsing, the family faces numerous obstacles and confrontations as they make their way towards perceived safety. They encounter acts of both kindness and brutality in a world driven to the brink, testing their resolve and unity. The journey becomes a harrowing race against time as they struggle to stick together amidst mounting peril and uncertainty about their fate.