Time in the galaxy has stopped running in its normal course. That can mean only 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 with the Guardian.