Written by Ian Stuart Black
Directed by John Davies
The TARDIS crew visits a human colony that appears to be a happy place run along the lines of an enormous holiday camp. In fact, this seemingly ideal society has been infiltrated and taken over by a race of giant crab-like creatures called the Macra.
The brainwashed inhabitants are forced to mine a gas toxic to themselves but vital for the Macras’ survival. Ben falls under the Macra's malign influence and turns against his friends. He eventually regains his senses, however, and under the Doctor's guidance destroys the gas pumping equipment, thus killing the Macra and restoring freedom to the colonists.
Now free from the influence of the Macra, life in the colony returns to normal, with the community heaping honours on the TARDIS crew. During the celebrations, the travelers dance their way back to the TARDIS.
Sometimes you come across a Doctor Who story that you wind up loving even though you know it's not actually very good. You know there's flaws there, you can see them, but something about the story connects with you, so you ignore those flaws and love the story anyway.
The Macra Terror is one of those stories for me. Yes, I know there are flaws, but the things I love about this story, I love so much that it papers over any cracks in the foundation.