The mark of a great episode of time-traveling dramedy Doctor Who: I couldn't think of which "Aha!" moment to include as a little clip with this recap. I settled on the episode's weird little homage to The Matrix (sans blue pill) because it was just such a great little moment, and it opened up the whole episode. But there were a lot of great moments — each pertaining to their own strands of the story — in this episode. Details, and spoilers, below.

Doctor Who Gives A Glimpse Of Its Own Future

I was actually a tad nervous about the two-parter that begins with "Silence In The Library," becuase I (and others) had built it up so much. Writer Steven Moffat, the writer of "Blink" and "The Empty Child," would come save us from the dreariness of Doctor Who season four with a lovely return to form. Luckily, Moffat pretty much delivers, with an episode that feels like a slow burn at first, until it starts unleashing plot twist after plot twist with terrific dexterity.

The stakes were even higher this time around, because we all know Moffat is taking over as the show-runner of Who in 2010. So it's hard not to see this episode as giving hints to where Moffat's version of the show might be heading.

Doctor Who Gives A Glimpse Of Its Own Future

Most obviously, the new character of River Song (Alex Kingston from ER) has a huge "recurring character" flag over her head. She's had some kind of intense relationship with the Doctor in his future (and her own past), and now their timelines have crossed. I would not say no to a few years of Doctor-and-River adventures, based on this one episode — she seems like a good foil for the Doctor, almost his equal in knowledge, but also independent. She's comfortable in the Doctor's world, but can obviously also do without him. And he's trusted her enough to give her his diary and his sonic screwdriver.

(And I would bet that the next time we see River, we'll get the reverse of this scenario, where the Doctor now knows her, but she doesn't know him. This is the sort of thing the Blinovitch Limitation Effect is supposed to prevent.)

Doctor Who Gives A Glimpse Of Its Own Future

But including River in the episode also opens up the Doctor's story in all sorts of other ways. Like: he's young for a change. I've lost count of how many times in the RTD era we've heard the Doctor refer to himself as old. (Or someone else referring to the Doctor that way.) It's a refrain. Now, all of a sudden, his best years are ahead of him — which is really a much more interesting way to pitch the show, if you think about it. (Of course, if he's really only got three more lives left, then objectively, he is old.) The idea of the Doctor getting hints about his own future has only been played with a few times before on the show (most notably in 1989's "Battlefield") but it's exciting to get hints about adventures we haven't seen yet.

And, of course, it's nice for the Doctor not to know everything for a change as well. Plus all the talk about "spoilers" and how bad it is to peek ahead, was obviously very gratifying.

The main story of the episode, of course, is only tangentially about River Song and the Doctor's future relationship with her. Instead, it's about a deserted library where sentient shadows are killing everybody. All of the stuff I'd heard in advance about "count the shadows" and "data ghosts" had sounded very similar to previous Moffat outings, especially last year's weird rules in "Blink" about not being able to close your eyes, or the stone angels will move. Actually watching the episode, however, it didn't feel like a retread at all, and the business with the shadows moving around felt sufficiently creepy, and yet logical, that it worked as a threat. Especially the moment where Proper Dave suddenly has two shadows, which made a nebulous threat suddenly very, very concrete.

Doctor Who Gives A Glimpse Of Its Own Future

And then there are the "data ghosts," stored brain patterns which continue to function for a while after death. They're a terrific metaphor for the slow realization that someone is gone forever — you think you can still hear them, still talk to them, for a while after their vital signs are wiped out. It's a nice way of twisting the knife of the show's two deaths, by making us linger over them. And then it makes Proper Dave much more scary, in a very "Are you my mummy?" way, once he's lurching around repeating his last words over and over again.

(I kept wondering if the "data ghosts" would be like the nano-genes in "The Empty Child" — a throwaway gimmick that turns out to be the key to the whole mess. Obviously people are being stored somehow, the way Donna has been "saved." We know Donna can't be dead. Probably.)

The other big mystery of the episode was the not-too-empty child, apparently in present-day Earth, who sees the library when she closes her eyes. Is she actually in the real world? Or is that just a Matrix-esque simulation that her consciousness has been ported into? Is she the library computer, or just connected to it somehow? I kept changing my mind about what role she was playing in the story, either innocent victim or secret ally of the Doctor — until the end, when she announced that Donna had been "saved," and she agreed to help the creepy Dr. Moon "save" the others. Which probably means she's part of the problem — even if unwittingly. Did she put all the humans, including Donna now, into some kind of electronic storage to save them from the living shadows?

Anyway, it was a lovely change of pace, and even the stuff that could have felt run-of-the-mill (new love interest for the Doctor, monster with weird arbitrary rules, child who can see the Doctor through her fireplacetelevision) somehow didn't, because the execution was awesome and you still couldn't tell where it was really going. Still very, very hopeful for the Moffat era of Doctor Who in a couple of years.