This story brings together the Miles O'Brien, Mac Calhoun and Jean Luc Picard of the Mirror Universe as they come together to fight the Klingon-Cardassian Alliance, which had taken over the Terran Empire a hundred years before. "Smiley" O'Brien must abandon Terok Nor (Deep Space Nine) in order to survive. Calhoun has Romulan allies at his disposal, among them the former Praetor. The Alliance had destroyed the Romulan's world. Then there's a secret group called Memory Omega, which was instigated by Spock long ago. They've planned out the downfall of the Alliance-- but timing is everything. They recruit a man who has lived for years among the Cardassians, someone who will have the leadership abilities to bring together these disparate fighting factions. This is the captain of the new Enterprise-- Picard.
Along the way we're also introduced to the Mirror Universe counterparts of Ezri Dax, Worf, and Saavik, Spock's protege who now runs Memory Omega from a hidden Genesis cave.
This book, like the most recent STAR TREK ENTERPRISE novel, ties up a complete storyline, which suggests Pocket Books is discontinuing these series. However, it presents lots of answers as to what happens to characters and sums up a lot of storylines. Recommended.