Well, I think everyone who deserved something bad happen to them had it happen to them here.
That includes that jackass squid monster Kroll.
Yes, forsooth, mighty Kroll doth attack the Swampie village! And verily, he hath taken many Swampie lives in the process, to the great delight of that evil Thawn!
Yeah, I’m not doing that anymore. Besides, there don’t seem to be any female Swampies, so I am guessing these guys are going to be extinct soon anyway regardless of whether or not the giant squid monster eats them.
But we do have two baddies. There’s religious fanatic Ranquin, the Swampie’s chief, and there’s racist fanatic Thawn, who would just assume nuke the whole site from orbit so long as he gets his precious, precious methane. Heck, he’ll even kill one of his own techs, the one played by K9’s voice, for being reasonable and not wanting to commit Swampie genocide.
While all this is going on, Romana and the Doctor manage to get back to the refinery. Also, so do the surviving Swampies. As Thawn loses it more and more, the Doctor does try to reason with the unreasonable (after sabotaging a missile Thawn is trying to fire at Kroll/the Swampies), but the Swampies kill the guy first.
He had it coming.
Besides, Kroll is now attacking the refinery itself, and there’s only so much that can be done. Even more of the Swampies realize Kroll is not much of a god so much as he’s an unreasonable monster. You know, everyone except Ranquin, who decides to talk to Kroll.
Kroll eats him.
So, can the Doctor save the day? He does have a theory. First, he has all the refinery’s equipment turned on to make enough noise to keep Kroll busy. Then he borrows the Time Key Fragment Finder Wand from Romana to test a theory. Climbing the refinery’s stairs to the topmost tower, he sees Kroll’s giant single eyeball glaring at him, and as a tentacle tries to squeeze the life out of him, he pokes the Wand at the eye, and that turns into the fifth fragment, killing Kroll in the process.
See, the holy book the Doctor borrowed mentioned a previous high priest was swallowed by Kroll along with a holy relic Said relic was obviously the Fragment, and that allowed Kroll to grow to gigantic size.
Then all he has to do is shut off the rocket that normally is full of methane on its standard delivery because with all the damage to the refinery, it’ll explode the whole refinery and everyone around for miles. Yes, the Doctor can do that.
Without Kroll, the refinery has no methane to mine. So, the Swampies get the land back, and there will soon be more normal giant squids around now that Kroll has exploded into a bunch of much smaller ones. So, a job well done, provided the Doctor can remember where he parked the TARDIS.