Adm. James T. Kirk (William Shatner) has defeated his archenemy but at great cost. His friend Spock has apparently been killed, the USS Enterprise is being scrapped, and starship physician Dr. Leonard "Bones" McCoy (DeForest Kelley) has taken ill. McCoy's odd behavior is evidence he's harboring Spock's katra, or animating spirit, and Kirk seeks to take the Enterprise back to the Genesis Planet and find his friend. Rebuffed, Kirk takes dramatic action that results in war with deadly Klingons.