Land of the Dead

Thomas Harlan returns with a third novel in his In the Time of the Sixth Sun alternate history series.
It's a small change in our history: Imagine that the Japanese first made contact with the Aztec Empire. Instead of smallpox and Christianity, they brought an Imperial alliance, samurai ethics, and technology to the powerful and bloodthirsty Aztecs. That culture sweeps across the world, conquering and ruling. By the time of these books, the Emperor in Mexico City rules not just the entire planet Earth, but a growing interplanetary empire as well.
But the galaxy is not a hospitable place, and there are other powers, both new and very, very old, that would stop the spread of the power in Anahuac.
A weapon of the Old Ones, from the time of the First Sun - the earliest discovered Galactic Empire, now millions of years gone - has been found in a distant region of space. It has annihilated three Imperial cruisers. It must be investigated, tamed, or destroyed to keep it from the hands of opposing powers. Gretchen Anderssen, freelance archaeologist and specialist in First Sun artifacts, has been hired by her old mentor, Green Hummingbird, agent of the Anahuac Secret Service, to join him in the mission.
Susan Kosho, of the Imperial Navy, has been promoted to captain and given her own ship - a powerful new vessel with new technologies. But she is immediately dispatched to the artifact.
Gretchen, Green Hummingbird, and Kosho will be joined in this mission by other old friends and enemies, both expected and unexpected.