Capt. James Kirk (William Shatner) and the crew of the USS Enterprise are carrying Klingon Chancellor Gorkon (David Warner) to Earth to negotiate a peace treaty with the United Federation of Planets. The ship appears to fire on a Klingon vessel, and Gorkon is killed in the subsequent confusion. Kirk and the ship's doctor, Leonard McCoy (DeForest Kelley), are arrested for murder, leaving Spock (Leonard Nimoy) to figure out who is behind the attack and save the negotiations.