Operation: Annihilate!

TOS Season 1 Episode 29
Air Date: April 13th, 1967

The final episode of season one. The Enterprise is tasked to study a trend of mass insanity that has been sweeping along an area of space spanning hundreds of years. It is a bit odd that they are only investigating it now.

They arrive at the planet Deneva, a Federation colony to discover they can't communicate. They do find a space ship heading to the sun but they couldn't get to it in time before it gets destroyed. They do get a message from the ship saying "We're free". It turns out that Kirk's brother Sam was part of the colony.

They beam down to discover that everyone is staying inside and are attacked by people who are telling them to leave the planet. They stun them and then try to find Sam. They find Sam's wife hysterical and Sam is dead. His son unconscious. They take his wife and son to the Enterprise and discover that they are in tremendous pane which is what is causing the insanity. Sam's wife tries to explain what happens but the more she talks to more pain she is in until she eventually dies.

They go back to the planet and discover these small slime like things that seem to be able to fly short distances. They shoot one with a full phaser blast and it merely stuns it. When they go to leave, one of them flies onto Spock's back and injects him with a toxin.

McCoy discovers that the toxin is actually an extension of the alien nervous system and it grows inside the host causing extreme pain. Once it is in you, there is no getting it out as it is all over. Spock eventually uses his Vulcan abilities to overcome the pain and goes down to the planet to capture one of the creatures.

Studying the creature shows it is almost indestructible. It turns out that each creature is a single cell and that they work together was on giant consciousness. Kirk eventually realizes that the reason the sun helped free the others was due to the bright light it emits and then they use light to free Spock from the creature. They then set up satellites to save the people on the planet, though commits genocide on these creatures.