Land of the Dead

This is the third book in Thomas Harlan's In the Time of the Sixth Sun series. It can be read alone, but you will get more out of it if you read the preceding two books first (Wasteland of Flint and House of Reeds). The stories take place in an Aztec/Japanese dominated human star empire in the far future of an alternate history line. (All three books are good stories.)
I really like Harlan's writing style. He doesn't go in for info-dumps, but rather lets the details of things such as the back story and the political situation come out naturally through the characters actions, observations, decisions, and memories. (Reminds me somewhat of Vonda N. McIntyre in that respect.)
The book follows the fortunes of four main characters: Susan Kosho, an Imperial Mexica Navy captain; Gretchen Anderssen, a Danish archeologist; Mitshharu Hadeishi, a former Navy captain who has lost his ship; and Green Hummingbird, a very devious and dangerous Imperial agent. Things can get very dangerous out on the rim of the empire, and humans aren't necessarily the toughest species out there. The Imperial scout service has found an ancient and enormous artifact that might date back to the time of the First or Second Sun. It promises enormous power but is also enormously dangerous. Naturally, the empire dispatches an expedition. The two alien races that decide to get in on the game complicate things, as do the (at least) four human factions with their own agendas. Things get very complicated and very violent with lots of naval combat. I don't think it is a spoiler to say that not everyone makes it back.
If you like Jack McDevitt's books, you will probably like this one.