A massive meteor shower destroys the orbiting Space Shuttle Atlantis and bombards a swath of land from America's East Coast including New York City through Finland. NASA discovers that a rogue comet the size of Texas passed through the asteroid belt and pushed forward a large amount of space debris. The core of the comet, now considered an asteroid, will collide with Earth in 18 days, creating another extinction event. NASA scientists, led by Dan Truman, plan to trigger a nuclear detonation 800 ft inside the asteroid that will split the asteroid in two, driving the pieces apart so both will fly safely past the Earth. NASA contacts Harry Stamper, considered the best deep-sea oil driller in the world, for assistance and advice. Harry returns to NASA, along with his adult daughter Grace, to keep her away from her new boyfriend, one of Harry's young and rambunctious drillers, A. J. Frost. Harry and Grace learn about the asteroid, and Harry explains he will need his team, including A. J., to carry out the mission. Once they have been rounded up and the situation is explained, they agree to help, but only after their list of unusual rewards and demands are met.
NASA sets plans to launch two military space shuttles Freedom and Independence with redundant equipment to increase the chances of success; the shuttles will refill with liquid oxygen from the Russian space station Mir before making a slingshot maneuver around the Moon as to approach the asteroid from its backside where the target bomb site is located. NASA puts Harry and his crew through a short and rigorous astronaut training program, while Harry and his team re-outfit the mobile drillers, "Armadillos", for the difficult job.
The destruction of Shanghai by an asteroid fragment forces NASA to reveal their plans to the world. The shuttles are launched and arrive at Mir where its sole cosmonaut Lev helps with refueling. A major fire breaks out near the last stage of transfer, and the crews including Lev