Episode Title: "YESTERYEAR"
Production Number: 22003
Original Air Date: 09-15-73
Stardates: 5373.4, 5373.5, 5373.9, Twentieth day of Tasmeen, 8877
The U.S.S. Enterprise is in orbit of the planet of the time vortex, where the crew is assisting a team of historians using the Guardian of Forever to investigate Federation history.
When Captain Kirk and Commander Spock return through the Guardian of Forever from a mission observing the dawn of Orion civilization, no one recognizes the Vulcan officer. When Kirk and Spock beam up to the Enterprise, they find that an Andorian officer named Commander Thelin has been the ship's first officer for five years.
Kirk and Spock realize that they have returned to a different timeline from the one they left when they visited Orion's past. In this timeline, Spock died as a child at age seven, on the twentieth day of Tasmeen, during the kahswan maturity test, and never became a Starfleet officer. The scientists were using the Guardian to scan that period, thirty years in Vulcan's past, while Kirk and Spock were in Orion's past.
Spock remembers that, when he was a child, his cousin, Selek, saved his life on the twentieth day of Tasmeen, Vulcan year 8877, when Spock was attacked in the desert by a wild animal. Kirk and Spock theorize that Spock had traveled from the future and posed as Selek to save his own life as a child, but in this timeline, Kirk and Spock were in Orion's past when that time period of Vulcan's past was re-played through the Guardian, so Spock did not save himself.
In order to restore the timeline Spock remembers, he travels through the Guardian of Forever to the month of Tasmeen, thirty Vulcan years ago, near the city of ShiKahr. There he meets Sarek and his young son, Spock, who is teased by other Vulcan children for being half-human.
Spock follows his younger self into the desert, where a le-matya attacks young Spock's pet sehlat, but the older Spock subdues the le-matya before it can kill his younger self. In a divergence from the timeline Spock remembers, young Spock's pet sehlat is injured by the le-matya's poison claws, and cannot be saved, and young Spock decides to let it die rather than live in pain.
Having saved his younger self, Commander Spock returns through the Guardian of Forever and finds the timeline restored.
Factoid: The kahswan ordeal is an ancient rite of warrior days. When Vulcans turned to logic, they maintained the tests of courage and strength to keep pure logic from making them weak and helpless. The test of adulthood requires a child to spend ten days in the desert of Vulcan's Forge, without food, water or weapons.
*Commander Thelin, Sarek, Amanda, Guardian of Forever
Alien Races: Andorian, Vulcans, *Vulcan sehlat, *Vulcan le-matya, *Aurelian
Starships: U.S.S. Enterprise NCC-1701
KEY: [brackets]=illusions *star=first appearance