Spock is unusually restless and ill-tempered. After he throws a bowl of soup at Nurse Chapel, Kirk insists on an answer and Spock reveals that he is in the early stages of Pon Farr, the Vulcan time of mating that occurs once every seven years. He must return to Vulcan to mate or he will die. Kirk goes against Starfleet and heads toward his friend's home planet, but the Vulcan ritual doesn't go as planned and Spock must soon fight Kirk to the death.
The Enterprise is heading to Pollux 4 on a archeology mission when a large energy field in the shape of a giant green hand stops the Enterprise dead in space. A giant figure appears out in front of them, claiming to be the ancient Greek god Apollo. He insists that Kirk and a landing party down and Kirk agrees, only to discover that Apollo wants them to worship him... whether they want to or not.
The Enterprise responds to a distress call from the planet Mulour, only to find the entire civilization has been destroyed. Then a small probe with incredible weaponry and defense capabilities attacks the Enterprise. After Kirk identifies himself, it agrees to be beamed aboard to make contact. The probe, Nomad, was sent out to explore the far ends of the galaxy, but it has altered and is now dedicated to seeking out and sterilizing life forms. Only the fact that it believes Kirk is its creator is keeping it from destroying the Enterprise... and it starts to see through the deception.
The Enterprise is on a mission to convince the Halkan Council to allow the Federation to mine dilithium crystals on their planet. Kirk, Scotty, McCoy, and Uhura beam back up to the planet, but while doing so, an ion storm causes them to rematerialize in a parallel universe. There officers advance through assassination and the Empire plunders and pillages every planet they can find and destroys anyone that gets in its way.
Kirk and a large landing party beam down to explore the beautiful garden planet of Gamma Trianguli 6. But the planet turns deadly when the party are killed by dart-shooting flowers, exploding rocks, and precision lightning strikes. The party captures one of the primitive locals who insist that their god Va'al rules over the planet... and it is angry with the newcomers who seek to destroy Paradise.
The Enterprise responds to a distress call in the L370 system and discovers that something has destroyed almost every planet in the system. They also find its sister ship the U.S.S. Constellation, which has been badly damaged. The captain of the Constellation, Commodore Matt Decker, says that his crew evacuated to one of the pulverized planets and was lost, and the attacker was a giant robot "doomsday machine". Kirk is stranded on the Constellation when the doomsday machine attacks again, and the shell-shocked Decker tries to take command of the Enterprise to lead a futile attack.
A landing party beams down to Pyrus 7 to survey the surface. The Enterprise loses contact with them, then gets a message from one crewman, Jackson, asking to be beamed up. When they do, he's found frozen dead and a voice speaking through him tells them to leave. Refusing to abandon Sulu and Scotty, Kirk, McCoy, and Spock beam down to encounter witches, castles, a black cat, a warlock, and a sorceress, all determined to have them leave.
The Enterprise is taken over by a new crewman, Mr. Norman, who redirects it to a distant planet. He booby traps the controls and the crew is forced to wait and see where they end up. They end up at a planet populated by androids... and their old adversary, Harcourt Fenton Mudd, who wishes to use the Enterprise to get away.
Kirk, Spock, and McCoy transport an ailing Commissioner Nancy Hedford from Epsilon Caneris 3 to the Enterprise. Their shuttle is intercepted by an ionized hydrogen cloud and forced to land on a small inhabitable planet. The shuttlecraft engine is damaged and while they struggle to make repair, they come into contact with a person of great historical meaning to the Federation, thought to have been dead for 150 years.
The Enterprise is transporting ambassadors and mediators to a conference on the planet Babel. There the delegates will determine if admitting Coridan to the Federation is feasible. While in route, one of the ambassadors is cuddled and the prime suspect is the Vulcan Ambassador, Sarek... who is Spock's father.
Kirk negotiates with the highly honor-bound natives of Capella 4 to obtain mining rights. The Klingons interfere in the tribe's politics and attempt to secure their own deal. When the tribe's leader is killed, his wife must share his fate to destroy any possible heir, until Kirk saves her. Kirk, Spock, and McCoy escape with the pregnant woman, Eleen, and must keep one step ahead of the ruthless Capellans and the angry Klingons.
Kirk and a landing party investigate a colony on Gamma Hydra 4 and find that most of the residents have died... of old age. They bring the last few survivors on board the Enterprise where they die, but it soon becomes apparent that everyone from the landing party is showing the same signs of accelerated aging. Only Chekov appears immune and they must find a cure before they all die of old age.
Kirk and a landing party beam down to examine tritantium deposits and are attacked by a gaseous creature that feeds on red blood cells. Kirk remembers the creature as one that he fought - and failed to destroy - earlier in his career and where his mistake killed half the crew. Now the creature is stalking the Enterprise and Kirk is determined to destroy it no matter what the cost.
Scotty, Kirk, and McCoy beam down to Argellius II for shore leave. Scotty becomes attracted to a belly-dancer and goes on a romantic walk with her. Later the belly-dancer is found embraced to death... with Scotty holding the hug weapon and claiming to suffer from amnesia. The Argellians are eager to put Scotty on trial but Kirk believes someone else is responsible and holds a hearing to get at the truth.
The Enterprise goes to Deep Space Station K7 responding to a distress call. After reaching the station, Kirk finds out the distress call to be unwarranted and the Klingons have come there looking for some shore leave. Kirk must maintain order as the Federation and Klingon tension is high. That and the fact that the station and the Enterprise are being overrun by small furry animals known as tribbles.
Kirk, Uhura, and Chekov are kidnapped away from the transported pad as they prepare to beam down to Gamma 2, an uninhabitable plant with an automated station. The party appears on a completely different planet and are taken prisoner. Spock must find out what happened and try to find where the landing party has gone.
Kirk and the Enterprise try to make contact with the people of Sigma Iotia II who have modeled their culture around the a book "Chicago Mobs of the Twenties" left behind by another Federation starship. Kirk and a landing party beam down into the middle of early twentieth century gang war and are taken prisoner after following the Prime Directive and not supplying weapons to the people.
The Enterprise is redirected to investigate the loss of communication with the Gamma 7A star system. While in route, Spock senses the destruction of a Vulcan manned starship, the Intrepid. Spoke says that all the Vulcans aboard have been killed. The Enterprise is ordered to Sector 39J to investigate what may have happened with the Intrepid after communication is lost with them as well.
Spock, Bones, and Kirk beam down to a planet whose inhabitants are far less technologically evolved. However, they realize that some of the planet's inhabitants are armed far beyond their natural capabilities and think that the Klingons may have gone behind the Federation's back and ignored the treaty about neutral planets.
The Enterprise receives a distress call from a planet that is too far away from Earth to have been visited by the Federation. When the Enterprise reaches the planet, a telepathic voice address the crew as his children and directs them to assume orbit around the planet. The planet's energy source is a hundred miles below the surface and Kirk and a landing party go and investigate.
The Enterprise arrives in a planetary system to find missing Federation historian John Gill. They are attacked by a nuclear missile from Ekos, even though that planet didn't have the technology capable of producing such missiles the last time a report was made. Kirk and Spock beam down and discover the planet is under a Nazi movement that involves the genocide of the neighboring planet Zeon.
An Enterprise landing party beams down to investigate a distress call. Two humans appear and thank Kirk for their speedy response to the distress call. They then demand that Kirk surrender the Enterprise and paralyze the party before they can stop them. The survivors are from far away and need the Enterprise to reach their home.
While on a routine expedition to Omega 4, the Enterprise arrives to find another starship, the U.S.S. Exeter, in orbit circling the planet. Kirk and a party go to the ship and find it abandoned and everyone on board completely drained of water leaving behind only bodily minerals. They check the log and are warned not to return to their ship, so go to the surface of the planet and find Captain Tracey... who is now in charge of the local civilization.
Kirk and the Enterprise are ordered to a space station and told to evacuate the crew on the station. Kirk is informed that the Enterprise will be the test vehicle for the M5 Multitronic System, a super computer designed to replace a crew. It is to be tested in battle simulations, but as the mission progresses it refuses to give up control.
Stardate 4040.7: The S.S. Beagle, missing for six years, is found as debris near Planet IV of System 982. Kirk, Spock, and McCoy beam down to the planet to investigate and find a ragged group of fugitive slaves trying to stay hidden from the police. These "sun worshippers" distrust the landing party but soon discover that they are not a threat. Kirk informs them that he is looking for another group of strangers led by a man named Merik. Merikus is the First Citizen of the Empire, but Kirk is not sure if it is the same man. Pursuaded to help them find Merik and his crew, the leader of the fugitives sends Flavius, an ex-gladiator, to be their guide. The landing party, however, is soon captured and led into the city where they discover a civilization much like 20th century Earth, but culturally similar to ancient Rome. The landing party find Merik, now First Citizen Merikus, who six years ago abandoned his ship and beamed his crew down to the planet. Those who could adapt survived, and th
Stardate not given: The Enterprise is sent on a mission back to Earth in the year 1968 to discover details about how the planet survived the arms race. While in orbit, the ship intercepts a transporter beam from an unknown part of the galaxy and beams the space traveler aboard. Surprised by what has taken place, the man identifies himself as Gary Seven and claims to be a 20th Century Earthman raised on an unknown world and trained to prevent Earth from destroying itself. Kirk decides to verify Seven's story before releasing him, but Seven escapes and beams down to the planet below. Kirk and Spock follow him to New York City, and Seven meanwhile discovers that two of his fellow agents have been killed in a auto accident. Seven is forced to complete their mission himself which is to sabotage an orbital nuclear platform, just low enough in the atmosphere to scare Earth leaders into prohibiting additional nuclear space weapons. Just as Kirk and Spock arrive, Seven beams out of his office a