A.C. Crispin 
Time For Yesterday [EPUB ebook] 

Time For Yesterday Time in the galaxy has stopped running its normal course. That can only mean one thing — the Guardian of Forever is malfunctioning. To save the universe, Starfleet command reunites three of its most legendary figures — Admiral James T. Kirk, Spock of Vulcan, and Dr. Leonard Mc Coy — and sends them on a desperate mission to contact the Guardian, a journey that ultimately takes them 5, 000 years into the past. They must find Spock’s son Zar once again — and bring him back to their time to telepathically communicate the Guardian. But Zar is enmeshed in troubles of his own, and soon Kirk, Spock and Mc Coy find themselves in a desperate struggle to save both their world — and his!