This is a science fiction novel by John Ringo and Julie Cochrane set in the Posleen war universe. It occurs some time after the end of the war, and deals with covert activities against one of our nominally allied species. The plot centers around the relationship between Cally and her sister Michelle, who has been raised by aliens and is a Michon Mentat.
There is a satisfying level of violence at the conclusion, and in short it is a typical Ringo novel.
Next up Ken Follett’s Pillars of the Earth.