This is a well written book that fills in a lot of info about the mirror universe. This book also uses mirror universe versions of famous (or infamous) characters from the prime universe. As far as I can tell, there aren't many contradictions between this book and official cannon

Having seen the original "Mirror, Mirror" and seeing the story line continued in "Star Trek: Deep Space 9"; I had always hoped a viable story would come about to fill in the gaps. The series "Enterprise" covered the beginning of the Mirror Universe eloquently. This book flows perfectly with "Dark Mirror" and ties the series of events leading to Star Trek Deep Space 9's Mirror Universe stories smoothly. I'm looking forward to the story that shows the inevitable conclusion of Spock's reform plan.