I loved this series as a kid, and get to share it now with my 10-year-old. In this one, humans attempt to take back their planet from the aliens who conquered it so long ago . . . but even if they succeed, what of the inbound starship bearing reinforcments? And can the human race continue to cooperate if the aliens are overcome, once the unifying threat is gone? Or will we revert to quarreling, warring nations and tribes?