A young amateur astronomer, Leo Biederman, discovers an unusual object in the sky, which turns out to be a comet. After further investigation, it is revealed that the comet is on a collision course with Earth, with the potential to cause catastrophic damage and mass extinction. The United States government, under the leadership of President Tom Beck, confirms the discovery and launches a plan, codenamed "Operation Messiah," to prevent the disaster. A team of astronauts, led by veteran Spurgeon "Fish" Tanner, is assembled to intercept the comet in space and attempt to alter its course using nuclear explosives.

Simultaneously, a tenacious TV reporter, Jenny Lerner, uncovers the existence of the comet and the classified operation. Her journalistic pursuit of the truth leads to its wide exposure, forcing President Beck to address the world about the impending danger and the international efforts to counteract the threat. As the mission to save the Earth progresses, the public grapples with the impending doom, while various human stories unfold. Families and individuals face the uncertainty and tumult of the future, exemplifying the resilience of the human spirit in the face of potential tragedy.