Twenty years after the first war for Earth between humans and their would-be alien exterminators, Earth has made light years of advancements in adopting things they've learned from the remnant alien technology, which they've not only used to rebuild their destroyed cities, but also to jump far ahead in terms of air and space travel, including to the moon. Those who helped save the planet have become heroes and celebrities, all of them had an aching feeling that they haven't seen the last of their newfound enemies in the universe, and with the long-dormant alien specimens and tech they've gathered since the battle seemingly coming to life in would appear that another battle must be imminent. Turns out they are right. A rag-tag crew of returning heroes and their offspring are not leading the charge to defend the Earth yet again against an ultra-powerful alien force unlike anything they've ever seen before (well, they have a bigger ship this time, and a bigger boss alien), who, according to this movie, want us out of the way so they can get to Earth's creamy magma center.