The Doctor: Well, you'd better introduce me.
Romana: As what?
The Doctor: Oh, I don't know... a wise and wonderful person who wants to help. Don't exaggerate.
The search for the Key to Time
takes the Doctor and Romana to the third moon of Delta Magna, a marsh-covered world where the indigenous tribesfolk worship a giant squid-god called Kroll. K-9 can't come along (it's too wet, and his actor is busy playing a mook). Things are complicated by the presence of a mining operation from Delta Magna, which is stealing the natural resources and angering the locals — and then it turns out that there really is a Kroll, the mining operation has woken him up, and he's more than a little grumpy. Kroll's really just an overgrown squid brought over by the colonists as a little one, but that doesn't make him less dangerous.
The head of the mining operation, Thawn, decides to blast Kroll with rockets, but the Doctor disables them just in time for the locals to mount an attack on the refinery and kill him. The gizmo the Doctor has been using to track the Key to Time shows it's Kroll — or maybe it's just inside
Kroll... Turns out Squidzilla has eaten a local relic which is the Key segment, and the Doctor uses his gizmo to transform it back again, which has the handy effect of turning one giant squid into lots of normal-sized ones. They retrieve the segment, prevent the whole rig from blowing up as an aftereffect, and leave the one remaining villain to sort things out with the tribesfolk on his own.
- Arms Dealer: Rohm Dutt, a smuggler from Delta Magna who's selling firearms to the local tribe.
- Chained to a Rock: The Doctor and Romana, by the local tribe.
- Crapsack World: it's an equal-opportunity-misanthropy depiction of colonialism where the colonists are all murderous racists or ineffectual wets, but the indigenous people are bloody-minded, backwards, sadistic, and worship a mindless monster just because it's big and scary. The ending gives the strong impression that the Doctor has absolutely no confidence in his standard "and now you must learn to live in peace together" speech and that the Swampies are going to execute the last surviving colonist as soon as team TARDIS is out of sight.
- Does This Remind You of Anything?: The setting resembles any number of situations in Earth history where relatively primitive nations are exploited by their more civilised neighbours. Except for the bit about the giant squid.
- Everything's Squishier With Cephalopods: A reeeaaaally big one.
- Family-Unfriendly Death: Thawn is impaled by a spear, complete with blood spewing through his fingers.
- Fantastic Racism
- Fantastic Slurs: "Swampy" and "Dryfoot" are what the miners call the locals and the locals call the miners, respectively.
- Giant Squid: Kroll.
- Human Aliens: The miners look just like (and may be descended from) Earth people. The locals also look a lot like Earth people, apart from being green.
- Human Sacrifice
- Hypnotic Eyes: The Doctor is unable to hypnotise someone into releasing him.
- Low Culture, High Tech: Thawn hires an arms dealer to sell defective guns to the natives as an excuse to get rid of them.
- Make Me Wanna Shout: Used by the Doctor to shatter a particularly tasteless window.
- Man in a Rubber Suit: The fake Kroll who tries to kill Romana.
- Occupiers Out of Our Country
- Old Shame: Robert Holmes has called this his least favourite of the Who stories he's written, describing it as rather dull. He was never a fan of "big scary monster" stories, and so was uneasy with the premise he was given, as well as the way the script was executed.
- Outgrown Such Silly Superstitions: Romana is very dismissive of Kroll and his titular power.
- The X of Y
- You Look Familiar: Philip Madoc, who played one of the miners, and John Abineri and Terry Walsh, who play tribesmen, each had multiple guest roles in Doctor Who over the years. Another of the miners doesn't look familiar, but is played by John Leeson, better known as the voice of K-9. (This was because John Leeson was contracted as a regular cast member, but having K-9 in a story with heavy location shooting in a marsh was never going to be practical.)