Preserver - William Shatner

In the Mirror Universe the tyrannical Emperor Tiberius, once captain of the ISS Enterprise, had great success turning captured alien weaponry to his advantage. Until, that is, his failure to seize the tantalising advances of the ancient First Federation. Now, in the more peaceful universe of the United Federation of Planets, Tiberius sees his second chance. And a new ally will help him take it - his alter ego for whom he has nothing but contempt - Starfleet Captain James T. Kirk.
Honorable, idealistic and decent, James T. Kirk is many things Tiberius is not. But he is also a man deeply in love with his wife - and Teilani is dying. To save her life, Kirk is prepared to compromise his ideals and enter into his most dangerous alliance yet. Battling Captain Jean-Luc Picard and a new generation of Starfleet heroes, Kirk must guide Tiberius to a long-abandoned First Federation base which conceals a power so great it will enable Tiberius to conquer the mirror universe - and his own.
But on that journey Kirk uncovers long-hidden secrets that raise the stakes far beyond the mere survival of family and friends. At the heart of their quest, something else is waiting: an object from a civilisation whose technology is far more advanced than any Kirk or Tiberius could hope to acquire, placed there for Kirk's eyes only by mysterious aliens who appear to have influenced life within the galaxy over eons of time - a message from the Preservers...