Third in Orson Scott Card's "Ender" cycle, "Xenocide" charts the events on the planet of Lusitania, home to all three sentient species in existence, two of which are not represented anywhere else in the universe. All living things on Lusitania are subject to a virus, the Descolada, which attacks and modifies the genetic information of the host and is evolving rapidly to the extend that combating it requires constant alteration of viricides in both non-native sentient species. Yet the native species, the Pequeninos, require the Descolada to survive, as it forms the means by which they transform into the different phases of their lifecycle. Any species looking to leave the planet would be required to take the Descolada with them, as it adapts and becomes a necessary part of any organism's genetic make-up. This is one of the main problems the planet is faced with, but the second is equally serious:
Lusitania is under threat of being annihilated by a fleet sent by Starways Congress, because the planet's scientists have broken the law of not interfering with alien species by helping the sentient Pequeninos to gain a foothold in agriculture. Rather than sending the scientists to trial and certain lifelong exile, the colony rebels and is thus to be turned into an example.
The narrative hinges on Ender Wiggin and those around him, with a wealth of emotional, scientific and philosophical conflict between unique characters against a background of questions more normally expected in moral philosophy.