[TOS] Season 2, Episode 6 (Netflix: S2 E6): The Doomsday Machine
This is another showdown episode done well. Maybe we’re just suckers for showdown episodes, but it seems like the original series is just really well suited to this type of plot. Doomsday Machine features a grieving, vengeful captain that separates it from the rest of these episodes.
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Read more at Memory Alpha
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Notes:

Enterprise finds a federation ship and it’s in bad shape. Also a solar system has been destroyed. High stakes!

They beam over to find the captain all by himself. He beamed his crew to a planet to try to save their lives but then something destroyed the planet.

It fires on them! Enterprise must be really strong to withstand blows that eat away at planets and destroy them

Meanwhile Kirk is still back on the Constellation trying to get it running. Someone is watching you, Kirk

Enterprise gets in trouble but Kirk and Scotty manage to repair the Constellation enough to bail them out

Decker steals a shuttlepod and takes it into the monster. They did a good job of Decker having a sympathetic position
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