"Doctor Who" is back to continue its sixth modern season. Earlier this week, I published my interview with showrunner Steven Moffat, which I highly recommend for serious "Who" fans, and I have a review of the mid-season premiere coming up just as soon as I memorize every room in the universe...

"Just tell me: the Doctor, is he worth it?" -River

Back when I reviewed "Silence in the Library" - the first time the Doctor met River Song, as opposed to the first time River met the Doctor (which was tonight) - I compared Steven Moffat's writing to that of comics superstar Grant Morrison, since they both tend to pack their work with ideas that all seem mad and intriguing enough to sustain an entire story on their own, but which instead become just one small part of the whole. "Let's Kill Hitler" was a classic example of this phenomenon, in addition to being a hell of a lot of fun.

I imagine you could build a whole episode around what it was like to grow up as Amelia Pond's best friend, or around a human-shaped spaceship crewed by miniaturized people(*), or the Doctor getting shanghai'ed back to Nazi Germany by someone with an eye on taking out Hitler, or the secret origin of River Song. Instead, they were all mashed together into the same episode, and Moffat and company mostly made all the parts fit together seamlessly without shortchanging anything of note(**).

(*) And one with a bridge and crew complement (423) that pretty closely resembles the original starship Enterprise, no?

(**) Hitler disappears quickly, but trying to kill Hitler is something of a time travel cliche, and ultimately it seems like the setting was mainly an excuse to see how Alex Kingston would look in a Nazi uniform. (And the answer is: as smashing as she looks in everything else.)

I say "mostly" because I'll be curious to see how or if the show deals with Amy and Rory's feelings of loss in future episodes. The conversation on the TARDIS suggests that the Doctor, Amy and Rory will stop looking for Melody now, and while that makes some sense from an integrity of the space-time continuum kind of way, their daughter was still abducted shortly after she was born, and while they ultimately got to know a version of her for years (Mels), and then have interacted with a more adult version of her on occasion (River), they've still lost out on the chance to raise their own flesh-and-blood, to see Melody take her first steps and say her first words, flub her line at the school play, etc., etc. And although Amy's feelings about having kids in the first place were unclear - in part because she was replaced by a puddle of goo for most of the pregnancy - that's not something to be cast off lightly. When I asked Moffat how he would reconcile Amy the bold, fun-loving heroine with Amy the grieving parent of the stolen baby, he told me, "It's dealt with." If this episode is all there is to that, I'm not sure I'll buy it.

If, on the other hand, Amy and Rory continue dealing with the emotions of this during the standalone episodes, then yay, especially since the episode itself was so bloody fantastic.

There wasn't a ton in the way of new revelations about River/Melody. People had been speculating for a while that Amy's baby and/or River was the regenerating girl in the spacesuit. All this did was to fill in and/or explain some blanks. Though she's the offspring of two humans, for instance, she's also the "child of the TARDIS," having been conceived there. The joke from the Weeping Angels two-parter about how someone other than the Doctor taught her how to fly the TARDIS is finally explained: the Doctor was busy dying, so the TARDIS herself did it.

In the meantime, we have entirely new questions - or, rather, we have an entirely new Question, "the oldest question in the universe, hidden in plain sight" - along with being told definitively that the older version of the Doctor from "The Impossible Astronaut" goes to that lake in Utah knowing exactly what's going to happen.

But despite the puzzle-like structure of many of Moffat's scripts, his version of "Doctor Who" wouldn't work without emotion, and it's here - specifically the emotions of River and the Doctor - where "Let's Kill Hitler" shone.

When River told Rory that she first met the Doctor when she was very young and impressionable, I think most of us assumed it was as a little girl, just like with Amy and Madame de Pompadour. Instead, it's just that she's very young into her latest - and final(***) - regeneration, having not decided on a new name, or wardrobe, or barely even a personality. (Though you can see obvious traces of River in Mels in retrospect.) River has spent her entire life being programmed to kill the Doctor, and she's already apparently done it once (if she can't regenerate anymore, than the girl in the spacesuit in 1969 is from earlier in her timeline), and she's on the verge of doing it again when the Doctor drags himself up off the TARDIS floor and forces her to spend some time around him and his general awesomeness, and in the process helps the former Melody Pond grow a conscience. The River after this will be a hellraiser, but she'll also winds up on the side of the angels (non-stone variety) whenever we see her.

(***) Though it's something of a bummer that River has to give up her remaining regenerations for the sake of the Doctor, we know from "Forest of the Dead" that the Doctor didn't expect to be able to regenerate from the fate that killed River, so her sacrifice for Ten makes the sacrifice for Eleven a bit less of a tragedy. On the other hand, the notion that River dies (or, at least, her physical body dies) to save the life of a man who would (apparently) later die at her (younger, out-of-sequence) hand suggests that she wasn't just sacrificing herself out of love, but guilt. And now I really just want to go back and rewatch every River Song episode again six times.

At the same time, though, the Doctor once again has to face just how much damage he's done to those he cares about. Forget exterminating his entire civilization; he's bollixed things up pretty good for all of his modern companions, who appear via a bit of archival holographic video as he asks the TARDIS to save him. Even little Amelia, whom he ultimately settles on over Rose, Martha and Donna, didn't get such a fair shake, what with the Doctor leaving her behind for the rest of her childhood, then returning in time to get her baby stolen by a cult bent on killing him. There are some heroes that might take pride on making this many bad guys hate him this much - see also the Axis of Evil who locked him in the Pandorica last season - but this obviously pains the Doctor. He wants to be a figure of fun and light and joy, and yet he keeps generating so much pain and hatred. Given recent events, it's easy to see him as someone who has no problem facing the final death, figuring he's caused enough trouble on this side of the curtain.

Instead, though, River saves him, the Doctor now has foreknowledge of Utah and the ability to plan, River has a destiny, and we got to experience one of the crazier, most entertaining episodes of the modern era of "Who." I'll take that.

No review next week, as I'll be on vacation and won't be seeing it in advance, but as for "Let's Kill Hitler," what did everybody else think?