Doctor Who/Recap/S21/E03 Frontios

"Range: Systems that could rebuild a civilization for us. Failure-proof technology. The Doctor: What happened to it all? Range: It failed."

Tegan wants to see something of humanity's future. So when the Doctor takes the TARDIS to Frontios, where sometime in the distant future the last remnants of humanity huddle together under semi-primitive conditions and occasionally get devoured by the ground or squashed by meteor showers, she insists on going out and checking up on them.

The Doctor, as usual easily talked out of disregarding Time Lord rules about not interfering, tries to help out. The locals, also in the usual way, treat the Doctor as a threat not a helper, but Turlough saves him by waving a hatstand in a threatening manner. Then it turns out the problem is giant insect aliens that used to attack Turlough's people too, and he has prolonged fit of scenery chewing. Eventually our heroes, together with the more reasonable Frontios-humans, fight the Tractators by outwitting their only articulate, thinking member, the Gravis. So that's all right. And they'll all get a nice break next, promise.

Tropes

 * Apocalypse How: Class X. Apparently the Earth collided with the sun somehow.
 * The Ark: Brought the humans to Frontios, then promptly crashed, leaving them without their advanced technology.
 * Big Creepy-Crawlies: The Tractators
 * Bound and Gagged: Norna in Episode Four.
 * Colony Drop: The meteor showers engineered by the Tractators
 * Deadpan Snarker: Five, by this point, has become almost as prone to this as his squabbling companions. E.g. "Oh, marvellous. You're going to kill me. What a finely tuned response to the situation."
 * Death Glare: Tegan manages a serious one when the Doctor, having passed her off as an android to save her from the Tractators, throws in a gratuitous (and uncharacteristically bitchy) bit about having got her cheap because "the walk is wonky and the accent's wrong".
 * Genetic Memory: With a large side of Incoming Ham, punctuated by BSOD-ing.
 * Good Samaritan
 * Gravity Master: The Tractators are powerful enough to displace the TARDIS' walls.
 * Gravity Sucks: And the Tractators use it to swallow people through holes in the ground.
 * Hive King: The Gravis. Without him the other Tractators become harmless.
 * Humans Through Alien Eyes: Apparently we're quite pathetic compared to Trions. Says Turlough. And Tractators. Says the Gravis.
 * Improvised Weapon: A hatstand, which also, thanks to the Doctor's rambling "Not hat people, are you?" talk, counts as Chekhov's Gun. It works, too.
 * I Was Never Here: And he means it literally.
 * Large Ham: Turlough in breakdown mode.
 * Made a Slave
 * Mistaken for Spies
 * Obstructive Code of Conduct: Time Lord rules about non-interventions go out the window early, for a change.
 * Plucky Girl: Norna
 * Purely Aesthetic Glasses: This story being written by the guy who gave the Fifth Doctor his specs, out they come again.
 * Schmuck Bait: How the Doctor dupes the Gravis.
 * The So-Called Coward: "Of course not...I'm Turlough."
 * Think Nothing of It
 * What Measure Is a Non-Human?: "You can't possibly take their side!"
 * You Can't Fight Fate: Turlough's professed motivation for going back.