Star Trek: Mirror Universe: Glass Empires is a collection of three relatively short novels set in the mirror universe introduced in the parallel universe originally introduced in “Mirror, Mirror” in the original Star Trek series:
- Age of the Empress, which follows the episode of Star Trek: Enterprise “In a Mirror, Darkly” in which Hoshi Sato becomes the empress of the Terran Empire
- The Sorrows of Empire, which follows the mirror Spock from “Mirror, Mirror“
- The Worst of Both Worlds, which features a mirror Jean-Luc Picard
Of the three novels, I preferred The Sorrows of Empire. I was never much of a fan of Star Trek: Enterprise, and the only regular characters from Star Trek: The Next Generation appearing in the third novel were Picard and Wesley (Crusher), who had no last name in the novel.
There are more novels set in the mirror universe:
I just started reading Star Trek: Deep Space Nine: Fearful Symmetry, in which characters also cross over to and from the mirror universe.