In the near-future, when the sport of boxing has gone hi-tech, Charlie Kenton is a washed-up fighter who lost his chance at a title when 2000-pound, 8-foot-tall steel robots took over the ring. Now Charlie earns just enough money piecing together low-end bots from scrap metal to get from one underground boxing venue to the next. When Charlie hits rock bottom, he reluctantly teams up with his estranged son Max to build and train a championship contender.

On July 2, a giant alien mothership enters orbit around Earth and deploys several dozen saucer-shaped "destroyer" spacecraft that quickly lay waste to major cities around the planet. On July 3, the United States conducts a coordinated counterattack that fails. On July 4 the a plan is devised to gain access to the interior of the alien mothership in space in order to plant a nuclear missile.