I am trying to remember a novel that I only read the first one or two chapters of. It begins on an alien world in the midst of a war. There were two types of aliens, with different names. It initially seems to be a war of annihilation; one group has captured a bunch of the others, who are sent to a facility from which none of the captured type ever emerge.
However, in discussion with a (human?) visitor, one of the alien leaders reveals that the two alien groups are only distinguished by whether or not they are infected by a mind-controlling psychic parasite. The captives being sent to the facility are being cured and coming out again.
The aliens have decided to hunt the parasites to their home world, to wipe them out. The home world is called Earth. That's when I stopped reading though.