Fifth big screen outing for the crew of the starship Enterprise. Kirk (William Shatner, who also directs and co-scripts), McCoy and Spock's shore leave is cut short when the latter's half-brother - Vulcan renegade Sybok - takes several important ambassadors hostage on the planet Nimbus. They race to the rescue, unaware that the kidnap is all part of Sybok's ploy to hijack the Enterprise and set out on a quest to discover the Supreme Being - God.

The Starship Enterprise is sent to escort the Klingon chancellor to peace negotiations with the Federation. When the chancellor is assassinated, the Klingons refuse to continue negotiations unless Captain Kirk (William Shatner) and Dr McCoy (De Forrest Kelley) are tried for the chancellor's murder in a Klingon court. Kirk and McCoy are sentenced to life imprisonment in a penal colony, leaving Spock in charge of the Enterprise and the only one who can solve the riddle of the murder.