The second half of the serial is much more fun. At the end of 3, the Ice Warriors show up, and there's the cliffhanger; in 4, we find out that they've been sent by the Federation to stop the infighting between the miners and the royals... only they totally haven't. The leader of the Ice Warriors wants to take over the planet and mine it's trisillicate for himself, while the engineer wants to control him, and make himself the most powerful and richest man in the galaxy.
Of course, the Doctor has something to say about that.
With the Doctor's help, the two factions of the miners work together, and the Doctor proves to them that the monster is an illusion used to scare them-- and even the ones who don't think it's a fake do think that he's now on their side, so they fight back. The miners bump off the Ice Warriors that are in the mine, while the Doctor saves everyone, and Sarah-Jane and Alpha Centauri contact the Federation and tell them what's going on.
In the end, Sarah-Jane's taught the Queen Who Looks Like Drew Barrymore that women can rule as well as men, the Doctor's gotten the miners and the royals together, and Alpha Centauri has gotten everyone in line with the Federation, and all is right with the world.
I wasn't too enamored of the first half, but the second had alot less mine drama and a lot more adventure. This is how I like my Doctor, and I like this half much better. Overall, though, I'd say this wasn't a strong serial, and there's alot of running around and getting re-captured, which we all know is a sign of padding out the episode.