Wow. This year's Doctor Who Christmas special explored some familiar territory for writer Russell T. Davies — and yet it was utterly mesmerizing, largely thanks to guest star David Morrissey. Spoilers below.

So. As you might have guessed beforehand, Morrissey isn't actually playing a future Doctor in last night's episode — although the show did a good job of teasing the possibility that he was a Doctor who'd lost his memory. Instead, he was Jackson Lake, a Victorian gentleman who lost his memory after the Cybermen killed his wife and snatched his son. He happened to look into an "info-stamp" about the Cybermen's enemy, the Doctor, and it imprinted on his mind. So he turned himself into a kind of Doctor-manque, complete with sonic screwdriver, TARDIS and companion.

It could have been tongue-in-cheek, but instead it was heart-rending, thanks to Morrissey's performance. He was, in a sense, the RTD-era version of the Doctor writ large — full of jokes and bravado, but with a terrible loneliness and grief lurking just under the surface. Just when I thought Davies couldn't wring one more story out of the idea that the Doctor is terribly sad and lonely, he goes and finds one. And it's quite a good one.

(It almost felt a bit unnecessary when the Doctor gave that speech at the end about why he always ends up alone. And yet, in a way, it capped off the episode's theme nicely and showed how some things never change.)

Sure, it's sort of a retread of the previous episode, where Donna got imprinted with the Doctor's knowledge and became the "Doctor-Donna," and it's also pretty close to the "Family Of Blood," where the kid had the fobwatch that whispered to him about the wonderfulness of the Doctor. But who cares, when it's this well done?

A New Look Inside The Doctor's Broken HeartsS

To be fair, David Tennant was also on rare form here — handling his "other self" very carefully and with a strange respect. His behavior towards the "other Doctor" changes only gradually, as he starts to realize this isn't actually a future self he's dealing with. He undermines the Morrissey Doctor here and there, but never outright starts to condescend to him. He takes to the "companion" role quite well. And even though I've heard Tennant say "I'm so sorry" a hundred times by now, he seems to mean it more than usual when he points out that Jackson Lake's luggage is too much for one person.

So, okay, David Morrissey isn't really playing a future Doctor here. Whatever. He could still take over the role when David Tennant leaves, right? I mean, there's precedent for it. Romana was so impressed with Princess Astra, silly name and all, that she chose to look just like her when she regenerated. It makes total sense for the Doctor to feel the same way about Jackson Lake. Right? Okay, probably not.

A New Look Inside The Doctor's Broken HeartsS

Oh, and there were Cybermen. Honestly, that part was sort of forgettable alongside the much more interesting "two Doctors" plot. I mean, there was nothing wrong with it. Dervla Kirwan was great fun to watch, and the whole Dickensian child-labor factory setting was cool. And, as various people have already noted, there was a cool "steampunk" vibe going on with it. Especially the ginormous engine with the huge gears. But it really only captured my attention in the last ten minutes, when the Cybermen suddenly turned into Megatron. Which, how can that be bad?

A New Look Inside The Doctor's Broken HeartsS

(Still — and this is really my only complaint — RTD's tics were in full effect here. Once again, you have a terrible enemy of the Doctor who is operating on "low power," or words to that effect, thus forcing them to turn people into pigs, or hide behind a game show satellite, or turn dogs into Cyber-shades and use infostamps, etc. etc. etc. I'm also a bit tired of the too-close links between each Dalek/Cyberman story, so that we're constantly meeting refugees from the previous battle. And then once again, the Doctor stops the Cybermen by forcing full awareness on (one of) them. These are fairly minor quibbles, but they're things that I'm not going to miss about the Davies era.)

A New Look Inside The Doctor's Broken HeartsS

In any case, back to praising the episode, which reminded me why I often love Davies' writing for Who. It was crazy and over-the-top and ridiculous and jammed full of fruit. But at its heart, there was a really moving, genuinely human story that managed to find something new to say about the Doctor. That's a pretty great achievement, after four seasons full of variations on a theme.