This is I think the next to last volume in the Star Wars Extended Universe series of books, by chronology. It is also, to my knowledge, the last book written by its author before he died unexpectedly a couple of years post-publication, certainly during the timespan when the EU was being gracelessly removed from Star Wars canon. There’s probably some kind of metaphor there.
Mercy Kill is about three things. Superficially, it’s about tying up loose political ends from the Fate of the Jedi series. Externally, it’s about a “wouldn’t it be cool if?” moment, the cool thing in this case being to bring back Wraith Squadron, the special ops branch of the New Republic’s navy. Being spec ops, they never used X-Wings as much as the rest of the navy did, but they were developed in the X-Wing series, and so here we are. (Also, it hasn’t been called the New Republic for a long time, but that doesn’t matter to you I’m sure, and being spec ops spy types, it doesn’t much matter to them either.)
Third and I’m sure most importantly, it’s about the horrors of war, the beauties of friendship, and the ways we cope with these things and the loss of them, and the long road of recovery. …okay, that’s a little bit overdone, but it’s not not about those things, and seeing as the series is all but ended, I’m feeling a little maudlin, okay? Oh, and fourth, like all the X-Wing books, it’s more than a little funny in the way that all good caper stories are. I guess I didn’t say, and wouldn’t have said before since I read the rest of the X-Wing / Wraith Squadron books years before there was a site to review them, but these are wisecracking, safecracking special ops people with hearts of gold, not grim dour special ops people who never leave a man behind. So the book is fun, which you would probably intuit from the Star Wars title, but might not from the mention of a special ops force as the stars.
Also, Star Wars isn’t always fun anymore, is it?