The five-year mission seen in The Original Series has finished, and the crew has moved on from the Enterprise. Captain James T. Kirk has been promoted to Admiral, Doctor Leonard McCoy has left Starfleet to become a veterinarian while other members of the crew have been given desk jobs. This has led engineer Montgomery Scott to become an alcoholic through boredom. Spock had returned to the planet Vulcan where he was seeking to control his human half.