It's fun to see how quickly the Doctor inserts himself into the running of Britannicus Base, as he follows the base's leader, Clent, around the Ioniser Room and realizes the Ionizer is about to explode -- but fortunately he's able to avert disaster. In this scene and the next we learn about how the Ice Age came about (an elimination of plants led to an elimination of carbon dioxide; er...) and how dependent Clent is upon the computer. He basically won't do anything without the computer telling him what to do. "Every decision is checked to eliminate risk of failure," Miss Garrett tells them. "Because, of course, all decisions, all actions, must conform to the common good." The Doctor clearly isn't convinced that such a reliance on computers is a good thing, but he doesn't immediately jump in and tell them all they're wrong, of course.
And the other major event in this first episode is that scientist Arden has discovered an unknown type of prehistoric man in the glacier. Except the Doctor notices that his helmet appears to have electronic connections. And as they start to thaw the strange man out, the creature awakens...
Episodes two and three are still missing from the archives, but the DVD has some rather nice animations in their place. From a different company (Qurios) than the last three stories we've encountered (all by Planet 55), they're actually quite good, other than being a bit paper doll-ish. And you can tell they've made an effort to use the telesnaps as close reference, which is a welcome move.
It's been remarked that you can lose episodes two and three and move from one to four without really losing much of the plot; this is true, but you also miss some character moments. In episode one we've been presented with Leader Clent as someone who relies completely on science and technology (as represented by the computer), with the clear suggestion that this is not a good thing. Episode two gives us Penley's friend Storr, who's so suspicious of anything technological that he won't even take medicine to heal his injured and infected arm: "You'd have stuffed me to the eyeballs with anti-this and anti-that. I'd have been flat on my back for weeks... Don't try scare me [sic] with all that scientific guff." So writer Brian Hayles is making it clear that the opposite extreme is just as bad.
Episode two also gives us the set-up that's going to drive the plot for the next five episodes: the Doctor tells them all that the man in the ice, the Ice Warrior, is from another planet -- which means that his spaceship is still out there and could cause a terrible nuclear explosion if the Ioniser interacts improperly with it. The rest of the story is going to be concerned with this worrying possibility. And then added into the mix is the Ice Warrior himself, Varga. He has a presence and a personality that comes through even in animation, and he doesn't feel like a stereotypical "monster", but rather a fully-formed character; he's concerned with rescuing his comrades in the glacier and contacting his home planet of Mars, and he's not going to let anyone get in his way. It's a determined characterization, and the cliffhanger reveals that Varga is thawing out four more Ice Warriors just like him...