One of the many things I love about Russell T. Davies' reinvention of Doctor Who is the fact that it's taken the time to question some of the show's most basic (and quasi-magical) tenets. What's more, it's done so in a way that's actually boosted our suspension of disbelief, rather than undermining it, which is no easy trick. In season one, we saw Rose freaking out over the fact that the Doctor's time machine had invaded her head to translate foreign/alien languages without her permission. And in season three, Martha gets into the question of how she can visit the past without stepping on the wrong butterfly or accidentally killing her grandfather. And now, in last Saturday's episode, we get to the biggest question of them all: why can the Doctor change history only sometimes? Spoilers ahead!
It's actually a really valid question, and one the show has waffled on quite a bit, ever since 1964's "The Aztecs," where the Doctor merely throws a hissy fit about the idea of Barbara trying to save the Aztec civilization but never explains why that would be different from stopping the Daleks or the Voord. The obvious answer is, "Because the Doctor spends so much time in one particular version of 20th./21st. century Earth, and he wants it to be the same whenever he goes there." But there's probably more to it than that, since he does occasionally meddle in Earth's past as well.
And so now we get a bit more of an explanation, and it's one which raises a bunch more questions — which is a good thing. The Doctor sees history as either fixed or in flux, and when he comes to a point that's fixed, he can't (or mustn't) disturb it.
And this episode actually gave me a reason to love Donna, who was one of the dozen or so things that annoyed me in last week's episode. She, more than any other recent companion, actually stands up to the Doctor. And she keeps doing it long after he's explained himself, and given his passionate speech, and shouted her down. She listens to all the Doctor's reasons, and then keeps telling him he's wrong. It's meant to be refreshing after the relatively worshipful attitudes of Rose and Martha, and it is.
I sort of assumed that the whole "we can't save Pompeii" plot would be dropped about two-thirds of the way through the episode, to make way for the real plot, about the rock monsters who want to do something or other. But then I was really happy to be proven wrong. The rock monster plot, as flimsy as it was, was simply there to advance the "we can't save Pompeii" plot. Which was a brave choice, and a really good one. In the end, because the rock monsters are averting the volcanic eruption that's "supposed" to happen, the Doctor actually has to take responsibility for his choice to let everyone in Pompeii die.
And the other reason it works so well is because the actors sell the story: You actually believe that Donna and the Doctor are anguished by this choice, instead of just sort of tossing it off.
And then there are all the little hints dropped in the scene featured above — like the thing on Donna's back. Is it, as some have speculated, something to do with the Racnoss, those spidery creatures we met in her first adventure? (In which case it wouldn't be the first time the Doctor's companion had a spidery thing on her back, since that happened all the way back in 1974's "Planet Of The Spiders.") Is the business about the Doctor's real name actually going to be significant? Are we going to learn his real name at last? (And no, I'm guessing it's not "Theta Sigma," the nickname he was called by in one episode years ago.) And then of course the hints that the return of Rose is significant to the overarching plot of the season.
And then there's the dangling plotline at the end, the family the Doctor finally chooses to save from the volcano. The one time he actually listens to Donna and does the nice thing instead of the smart thing. I will be horribly disappointed if that decision doesn't come back to smack him in the forehead in a future episode.
So — as I and many others predicted — this episode was a vast improvement on the fat-people-weird-babies episode last week. It definitely wasn't perfect. I couldn't quite tell you what the rock people's plan was, except that it involved circuit boards, and the mountain, and psychic people being turned into rock people. And the rock people were ridiculously easy to stop — with a water pistol, no less. But as I said earlier, the "main" plot of the episode was so transparently just an excuse to get into the issues the episode wanted to talk about, so it hardly mattered. Oh, and there was campiness, but it worked with the story. So yes, I'd say it was pretty decent, all told.
(And to those of you who are going to say it was better because Russell T. Davies didn't write it — his signature was all over it, including lots of little touches of humor. (The zany thing where Donna's Latin sounds like Celtic to the Roman people.) I wouldn't be surprised if RTD rewrote this script extensively — this is just an example of what RTD and his writers do well: a somewhat silly, fluffy story with an actual idea at its core, and an emotional crux that the characters actually get engaged with. It's only when he serves up pure fluff — and it's not even good fluff — that I get annoyed.