This is Book 2 in Shatner's Mirror Universe Saga. It's preceded by Spectre and followed by Preserver.
I read book one and was disappointed with the first 150-200 pages, but the last 100 pages or so were fantastic and totally left me wanting to immediately start this book.
The Mirror Universe subplot really comes into effect here. We are teased with Kirk's Mirror counterpart, Tiberius, at the end of Book 1, and then you see a great scene with him in the beginning of this book, but he doesn't show up again until the very end, even though the synopsis on the back of this book really pumps up the meeting between Kirk and Tiberius.
Kirk is still a tad whiny about his fiance/wife, Teilani, but overall this is a really good Book 2. Lots of really cool, very Star Trek scenes that kept the story moving. You even get scenes on Deep Space Nine and another subplot about this shadowy Starfleet operation. Like I said the book is really good and ends with a fantastic scene between Kirk and his Mirror double striking a dangerous bargain.
(And among the best of the lot IMO.)
I (reluctantly ?) admit to being a diehard Trekky when it comes to the shows and
the movies - but for a long time I turned my nose at the books...
It seemed to me they'd be cheap, crummy take-offs on the other media.
One day I found myself staring at a shelf full of them, and needed a Trek 'fix',
so I sat down and started to read; and was amazed at how mistaken I'd been.
Since then I cannot tell you how many of these books I've read, but I can tell
you for sure that out of many, many of them only one has been a disappointment.
If you enjoy Star Trek, you'll likely enjoy the books a surprising amount.
Live Long and Prosper !
All the great old characters and some new ones...