Doctor Who/Recap/S4/E07 The Macra Terror

"This is an emergency! Control must be believed and obeyed! No-one in the colony believes in Macra! There is no such thing as Macra! Macra do not exist! There are no Macra!"

- Control protests too much.

The TARDIS arrives at a human colony that seems happy enough but, as it turns out, the colonists are being mind-controlled by a race of giant crabs called the Macra. The Macra are using the humans to mine the toxic gases they need to survive.

Ben is affected by the Macra mind-control and starts to turn against the others, but the Doctor succeeds in breaking their hold and Ben destroys the gas-mining equipment, killing the Macra and freeing the colonists.

The Macra had a slightly surprising cameo four decades later in the Tenth Doctor episode "Gridlock".

Tropes
"Ben: They got that bloke all over the place like a blinking politician. Pete: He is our controller. We are always pleased to see him. He brings us encouragement. Ben: Oh, he's not a politician then!"
 * Deadly Gas
 * Extra-Strength Masquerade: The Macra so brainwashed the human colonists that an Extra-Strength Masquerade was relatively easy—until the Doctor turned up.
 * Giant Enemy Crab: The Macra
 * Muck Monster
 * Puppeteer Parasite
 * Security Cling: See the page picture.
 * Suspiciously Specific Denial: The quote above.
 * Take That:


 * Title Sequence Replacement: The first one in the series debuts here. It's also the first to use the Doctor's face.