This episode was written by Paul Schneider, who wrote two episodes of the original series.
The Enterprise is mapping a burned out supernova. Uhura picks up a weird signal with the word "Terratin", so they go investigate. They find a volcanic planet, and an impulse goes thru the ship. Everything seems normal, though, including the lab animals in sickbay. When sensors are run on the planet, everyone on the ship glows white, but no ill effects except the dilithium crystals--they are all fractured.
They then notice that tools, chairs, etc all appear to be growing. No--the ship's personnel are shrinking. The space between their molecules is decreasing. Spock notices that their uniforms are also shrinking, as well as the lab animals (I knew they would come in handy). So, it's only organic material that's affected. They will lose control of the ship once they get to 1 centimeter tall. That will take 29 minutes.
The crew starts getting injured--Sulu falls and breaks his leg, and Chapel falls into the aquarium. Kirk decides on a "Hail Mary" plan, beaming down to the planet. Spock notes that the transporter keeps a copy of their patterns--will it work to retain their size? It does--his rigged up communicator ends up doll size in his hand once he transports down. The volcanic lava takes it out, though. Kirk then finds a tiny city, just in time to transport back. He returns to what appears to be en empty ship--nope, they're just really tiny.
He sends a signal to the tiny city--he threatens to take it out with phasers. The leader of the city replies with a plea to stop--his bridge crew are down on the planet as well. Spock determines that "Terratin" is actually "Terra Ten", an earth colony long since lost. The attack on the ship was just their way of communicating. Now, the volcano is about to take out Terra Ten. The bridge crew beams up--and back to normal size. The rest of the crew beams down and back up--all with dilithium from the planet. The ship's phasers cut out the city from the planet and the whole thing is beamed up--they are on their way to a new planet to start their colony again.
Some things to look for:
- As in all the episodes, you can never see "the whites of their eyes", since it's the same color as their skin
- It's the first time we see this menagerie of test animals, including "gossamer mice" and "halo fish"
- An angry mustachioed crewman staring into his grande coffee cup
- Uhura looking rather provocative crawling around her instrument panel--maybe short skirts weren't the best idea for Starfleet
- The first and last reference to the material used in their uniforms, the futuristic "zenolon"
- The crew makes ladders and stilts with what appears to be wooden sticks--so they have an emergency wood supply on the ship?
- They spend a long time handling Sulu's broken leg when there's only 29 minutes to go
- I love how Scotty uses some string to run the transporter controls
Remember, you can play along by watching the show on Netflix!