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 McCoy -- 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 McCoy find themselves in a desperate struggle to save both their world -- and his!
I have read this book many times and with my iPad made it a lot easier. This is one of a few stories that starts fast of the Star Trek books but they are all very good. ;)