Well, giant rubber monsters might eat a Time Lord or two, but that doesn’t mean…wait, yes it would. The Doctor and Romana probably should get out of there.
That turns out to be easy when the people opening the gate realize it’s stuck, figure the beastie inside is stuck, and then raise the gate enough to try and let whatever it is get out. That works well enough as the Doctor and Romana scramble to safety. Apparently, for all her booksmarts from Gallifrey, Romana isn’t very knowledgeable about, oh, actually interacting with things in the universe.
That’s where the Doctor comes in because he quickly realizes what is going on.
It’s a real estate scam.
See, this exiled dictator, the Graff, may want to buy the planet that may have a large deposit of a rare and valuable mineral. The seller says he thinks the rock is useless, and even has a partner to confirm all this. All he wants is a large down payment to start the paperwork.
The Doctor overhears this and realizes there’s a scam. Also, the rare rock the Graff thinks he’s getting is the piece of the Time Key the Doctor is looking for. He and Romana manage to capture one of the two con men and lead the thief off to the TARDIS to get the piece and be on their way.
Well, this all seems rather easy. I thought this serial was four episodes long…
Oh, wait, the Graff realizes he’s been tricked and is waiting for the con man at the TARDIS. And he seems to think the Doctor and Romana are his accomplices. That probably won’t end well.