Wow - how have I never heard about this story before now? Things start auspiciously, with special title/writer/episode number inserts mirroring those of 'The Ice Warriors', but with the earlier serial's background icefields replaced by erupting volcanoes and oozing lava flows. The basic plot is compelling enough, with the Doctor, Liz and UNIT facing doom in a facility where the obsessed Professor Stahlman is boring his way through the Earth's crust to tap the vast energies beneath as an unlimited power source for the country - but a primordial slime is oozing from the machinery and turning those is touches into unthinking savages who can infect others with the same taint with only a touch; and the plant's computer indicates the process is dangerously flawed, but Stahlman is insistent upon faster and faster drilling. The performances are all top-notch, from Olaf Pooley's increasingly unhinged monomaniac Stahlman to Christopher Benjamin's well-meaning but helpless Sir Keith Gold, and especially Derek Newark (caveman Za all the way back in 'An Unearthly Child') as engineer Greg Sutton, who from the first finds himself fiercely antagonistic to Stahlman but engaged in a touching romantic subplot with his assistant Petra. The industrial locations, like the last story's, are excellent, and the Doctor gets to spend the spare moments when he isn't occupied in slanging matches with Stahlman tinkering with the TARDIS console using a borrowed nuclear power supply.
Then, the whole adventure gets tipped on its head. This last, apparently shallow side-story seems to be serving only to remind us that the Doctor is on Earth under sufferance and is still trying to get away again - but then he actually does and it totally surprised me. Slipping 'sideways' onto a parallel-universe Earth, he finds that everything is superficially the same except that he is in a totalitarian Britain where a republic came into being thirty years before and his associates, while physically recognisable, have become very different to their 'real-world' counterparts. Plus, the drilling operation is much closer to finally cracking the crust and unleashing the uncontainable power of the mantle layer beneath, and one thing unchanged is that this universe's Stahlman (or Stahlmann) still won't listen to reason since he too has been infected by the green goo and has only a little while before he reverts to bestial primitivism.
As well a completely refreshing the tale and giving it new impetus into the middle section of the seven episodes, this flipside world is an ingenious way of providing the Doctor with something to struggle against without throwing another 'invasion of the week' storyline at him: not only are the Primord creatures largely peripheral to the plot, but the green gunge is never followed-up or explained, and there are no alien enemies in sight - so what better way to subvert expectations and provide a unique slant on the Doctor's relationships with his friends than to make them the enemies? The decision to use the regular support cast in parallel roles where they become the Doctor's adversaries is inspired, as he suddenly finds he can no lomger trust those who were closest to him and really has to think on his feet to outwit them, escape this version of Earth and prevent the 'real' one being ravaged by the volcanic forces that will erupt from the mantle if the crust is breached by Stahlman's machine. We get a terrific chase in cars (Bessie also having been transported across), where Jon Pertwee really gets to show off his daredevil stunt driving skills, and across the oil refinery location's rooftops where the Doctor also has to deal with a loose Primord. His flight is ended when he makes the mistake of trying to communicate with this world's Liz Shaw, only to find that here she is a hard-bitten military type who wastes no time hustling him into captivity. Caroline John shines in the alternative role, with a noble streak appearing later through the tough exterior, and she is matched by John Levene's thuggish version of Benton in a performance far removed from the amiable Sergeant in the normal UNIT. Both, however, are outdone by Nicholas Courtney's jawdropping transformation into the moustache-less, eyepatch-wearing, sadistic Brigade Leader Lethbridge Stewat. The character's brutality and coldheartedness are brilliantly shown in the likes of the interrogation scenes with Shaw where the Doctor is really put through the mill (surely uncomfortable viewing for the younger Who fans), and when the action intermittently reverts to the 'real world' the familiar performances of Courtney and the rest seem shockingly different in comparison. The Brigade Leader's undesirable traits as mentioned are finally revealed as fronts for an inherent cowardice that is harshly shown up as the apocalypse overwhelms the parallel Earth, whereas most of the others find a kind of redemption in the face of approaching doom. Admittedly Stahlman, though equally looking different, retains most of his single-minded obsessiveness, but Section Leader Shaw's humanity breaks out in the end, and it is in the still-sympathetic version of Greg Sutton that the Doctor finds his ally and ice-maiden Petra finds her hero before catastrophe seemingly overwhelms them all. The Doctor, though, manages to escape in the nick of time and avert a similar fate for his real-world companions, and at the end of everything tries to get away again using the TARDIS console - but fails, is deposited on a nearby rubbish tip and sheepishly reconciles with the Brigadier to the laughter of Liz Shaw, in a nice final appearance for her in the series.
I was told beforehand it was going to be good, but I didn't expect it to be that good! Didn't start watching until 11:30 at night, but sat through seven episodes straight without a hint of falling asleep. Engrossing and marvellous.
Episodes watched: 170
Episodes still to watch: 552