(Planet of Giants episodes 1 & 2)
Season 2 starts not with a bang but with a fault: the doors of the TARDIS open in flight, worrying the Doctor and Susan quite a bit. It turns out the moment of materialization is the most dangerous moment in the TARDIS's flight and thus the worst moment for the doors to open. Still, everyone seems all right until they venture outside and realize that they've been shrunk down to an inch in height. The planet of giants is in fact Earth: "Susan, this means we're on Earth!" Ian exclaims excitedly, as if they haven't just been on Earth (maybe they haven't; again, Past Doctor Adventure writers take note).
The production crew have been kicking around the idea of an "incredible shrinking TARDIS crew" story since the very beginnings of Doctor Who, and this is the final result. It's an interesting serial, and the episodes are quite unlike anything we've yet encountered. The guest cast (which consists of a scientist, a man from the ministry, an unscrupulous businessman, and a cat) never directly interact with the regulars; they unknowingly cause problems by carting them around and such, but the fact that the TARDIS crew is only an inch tall rather precludes any sort of conversations or similar interactions being held. This means that the star of the show is less the characters and more the sets. Fortunately, Ray Cusick's designs are more than up to the task, with some really wonderful sets and elements (the briefcase and the plug chain are really nice, and the various insects are all quite good -- with special mention of the twitching fly in "Dangerous Journey"). This story is more about exploring an environment than anything we've gotten previously, and it's a nice change of pace. It does mean we get two rather odd-looking cliffhangers, even if they make sense in context. A close-up of a cat and a man letting water run down the drain don't sound particularly exciting, but they're both quite effective as part of the narrative. And a special mention for the ominous musical sting that accompanies the line, "There's a sink in the lab" -- marvelous. Oh! And this is Dudley Simpson's first score for the show, before he goes on to dominate the incidental music for the '70s. Not that it's particularly distinctive in comparison to any of the other scores we've gotten so far, but still, you have to start somewhere.
And one final note: "Planet of Giants" (the episode) features another use of "TARDIS sans 'the' ". Looks like this, combined with the uses in Marco Polo and one I didn't mention in "The Keys of Marinus", suggests that this was a stylistic choice in use at the time rather than one author's decision. Interesting, given how bizarre it sounds to our ears nowadays.