Oh, well, Lady Adrasta did a really bad thing there.
It’s a good thing the Doctor is there to clean things up for everyone else.
Why on Chloris would Lady Adrasta be terrified of the creature from the pit seeing as how it didn’t eat the Doctor?
Well, those two brainwashed scavengers put that metal disk onto the creature that Adrasta had briefly called a Tythonian, and, well, it can talk. Sure, someone has to hold a piece of the disk, and the voice is the same as the speaker, but the creature is intelligent.
Oh, not only that, it’s an ambassador from another planet, one with a lot of metal hoping to trade metal for plant life, something Chloris has in abundance.
And Lady Adrasta knew all that.
Some people just have to keep their petty monopolies going, and poor ambassadors like Erato here spend 15 years in a pit as a result.
K9 tells us Tythonians live for upwards of 40,000 years, so 15 ain’t no thang.
Of course, Adrasta claims it’s a lie, and a trick, and she wants her Huntsman to command the Wolfweeds to kill everybody, but that guy has some sense and instead has the Wolfweeds attack Adrasta, with a hungry Erato finishing the job.
So, problem solved, right?
Nope! It seems tipping an ambassador who comes to do some peaceful trade negotiations into a pit for long periods of time is one of the Tythonians’ buttons. They shot a neutron star at Chloris since, you know, it was an act of war as far as they knew.
But the Doctor has a plan involving a metal frame for the star, Erato using his own spaceship and metal-weaving abilities, and some neat tricks with the TARDIS to send that star off somewhere else. He needs to use some blackmail to get Erato to admit as much, and he needs to get the final piece of the ship back from the scavengers and Adrasta’s second in command, but the Huntsman helps out there, and the plan work even if Romana has to flip a few emergency switches.
Heck, Erato still makes the trade deal. Looks like the Huntsman is in charge on Chloris because he’s the only reasonable person with any level of authority left down there. That works for me and the Doctor, so off to the next serial.