I think you can guess where this is going.
The Doctor and Sarah seem awfully dim in their first scene. They've arrived in a quarry but pay no mind to the blaring sirens; it's not until almost the very last moment that Sarah realizes something's wrong. The subsequent scenes with all the rubble are suitably dramatic, and when Sarah finds a fossilized hand amidst everything, their troubles really begin.
This first episode does a nice job of keeping things moving. The Doctor works out that this hand is incredibly old, belonging to a silicon-based lifeform that appears to have come "fluttering down by itself" -- no spaceship fragments are found in the quarry rocks. Elisabeth Sladen, meanwhile, is clearly relishing the opportunity to play an evil (well, all right, possessed) character, giving a number of unnerving smiles and repeating "Eldrad must live" in a sing-song voice. And it's already in this first episode that the possessed Sarah causes a panic at the nearby Nunton nuclear facility94, taking the fossilized hand deep into the facility, right next to the nuclear reactor -- which leads into a great cliffhanger as Sarah opens the box she's carrying the broken hand in, and we see it regenerate and then begin to move...
The second episode, it has to be said, feels a lot like the second half of the first; Sarah is rescued and is cured of her possession, but that just means that someone else gets to be possessed and take the hand back inside. Well, to be fair, the first half of the episode involves working out how to get to Sarah, who's locked herself inside the reactor room, but once they free her it's someone else's turn. But there are some nice moments nevertheless -- Dr. Watson's phone call to his family when he thinks the plant is going to go into meltdown is often mentioned, and justly so. There's also the nice little callback to Terror of the Zygons where the Doctor puts Sarah in a trance again -- although this time it's to get her to remember what happened when she was possessed by the hand rather than slowing down her breathing to save oxygen.
But ultimately this episode shows us the Doctor's efforts to get Sarah and the strange hand out of the reactor room, and once he succeeds someone else steps up to take the hand right back in. Although the cliffhanger does show us something a little different from before, as Driscoll (the hand's new agent) succeeds in opening up the inner door and appears to walk straight into the nuclear reactor with the hand...
94 We're one letter off from the nuclear complex seen in The Claws of Axos (also by Bob Baker & Dave Martin), which as you'll recall was called Nuton. Nunton was originally going to be the same place, but then they apparently changed it, sticking the extra letter in to make it different. It's not clear why they changed it though -- were they worried about having two incidents at the same place in such a relatively short span? Not that the extra letter really fools anyone as to the original intention, mind...