200 years after man began exploration of the solar system, an event occurred. A comet was detected near Pluto that was entering our system and approaching Earth. It was calculated to miss the planet by 1.2 billion kilometers. As probes were sent to monitor the comet, the comet sought them out and destroyed them, after which it set its course directly for Earth. The UN scrambled to avert certain distaster by sending out orbit shifting (ATFI) missiles to stop the comet. Upon their impact, the comet's course changed and it crashed into the Moon. When probes were sent to inspect the damage, what they found was a host of alien military space crafts.