"Aww, they are so adorable, but we can't make them stay like this! Who would watch something featuring younger versions of starship crewmembers?"
The Enterprise is playing host to Commodore Robert April, the first commanding officer of the ship, and his wife, Sarah, the ship's first Chief Medical Officer. The Aprils are set to retire. Although the elderly Starfleet Officer has had a lot of adventures under his belt, he's a bit disappointed that it's all coming to an end. But one last adventure is in store when the crew catches a ship traveling at the unprecedented speed of Warp 36 (and backwards no less!), and wind up being pulled into a parallel universe while trying to stop it. Now Kirk and his crew find themselves in an alternate universe where time flows backwards, and have to escape from this reality before they all literally age out of existence!
This episode provides examples of:
- And the Adventure Continues: This was the last voyage of the TOS crew's Five-Year Mission before the movies.
- Continuity Nod: Commodore April refers to Kirk's previous mission to Beta Niobe, which occurs in TOS: "All Our Yesterdays". Kirk later refers to Minara, a star referenced in TOS: "The Empath".
- The process of using the transporter to revert Kirk, Spock, Bones, Uhura, and others back to their original selves, using the transporter's last-remembered stats on their bodies, was last used in TAS's "The Lorelei Signal" and "The Terratin Incident" (to revert old age and size shrinkage, respectively). It would also get used again a couple of times, in "Unnatural Selection" and "Rascals".
- Death by De-aging: Because time flows backwards in the anti-matter universe, characters die as babies and are born as old men. The Enterprise crew tries to escape before it happens to them.
- Fountain of Youth: The Enterprise and her crew end up in an anti-matter universe where time flows backwards, and the characters start to de-age. They're able to make it out by the skin of their teeth, but the senior staff all end up as toddlers, while Commodore April and his wife are aged down to their younger days. The two then use the transporters to restore everyone else to normal.
- Grand Finale: Of Star Trek at the time. Then The Motion Picture happened...
- Happily Ever After: Even though we never see them again, its implied that Commodore and his wife live out a happy retirement.
- Negative Space Wedgie: How they enter/exit the anti-matter universe. It happens when they tractor Fives ship and can't release it when she entered.
- One Size Fits All: The Enterprise's crew rejuvenate, and their uniforms shrink to fit.
- Remember the New Guy?: Commodore (formerly Captain and commander of the Enterprise) Robert April, who was mentioned as being the first Captain of the ship before Christopher Pike. April wouldn't appear again until Star Trek: Strange New Worlds.
- Sdrawkcab Name: In a bit of clever writing note, the name Arret is also "Terra" spelled backwards.
- Short-Lived Organism: Sarah has a flower with her, plucked from Capella 4, with a lifespan of only a few hours; it was just a seedling when taken aboard but is now withering. When the Enterprise finds itself dragged into an alternate dimension, the crew discovers that time runs backwards when Sarah's flower reverts to full bloom again.
- Status Quo Is God: Obviously Star Trek can't have its characters run the flagship of Starfleet as babies, so they're restored to their proper ages using the transporter. Robert and Sarah April also return themselves to their original ages, despite the latter's suggestion that they could stay young, because the former has no regrets about what he did with his life, and wouldn't change a thing about it.
