There are times when it’s very hard to write about Doctor Who.

Especially this season, one of the best in YEARS. A season when most episodes have been so good that it’s a real challenge to come up with a review that doesn’t consist almost entirely of “HOLY CRAP” and “OMG” and “SQUEEEEEEE!”

But episodes like “The Girl Who Died” make that a great problem to have.

A little flashback (which I can get away with because we’re talking about a time-travel series): Back in February I had the honor to meet Jamie Mathieson at Gallifrey One in Los Angeles. Of all the guests at the convention, he was the one I was most excited to meet – Mathieson wrote my favorite episode from last season, and “Flatline” was even more awesome for being the first episode he’d written for the series.

It wouldn’t be the last, of course. On the strength of his first script for Series 8, Mathieson would land another, the almost-as-good “Mummy On The Orient Express.” Between that story and “Flatline,” it’s no surprise that fans were pretty keen on seeing him come back for Series 9. Which brings us to now.

While Steven Moffat is credited as co-writer, “The Girl Who Died” feels like Mathieson’s work through and through. There’s dialogue with the same sharp wit, villains with the same creepy vibe, and a story with the same emphasis on hard choices and hard consequences.

The episode begins on an almost Bondian note, at the end of an unrelated adventure with Twelve and Clara and that orange spacesuit we’ve seen so many times that it really should be declared an official companion. It’s a great scene – tense, funny, and over before it can outlast its welcome.

What follows is even more interesting. In the process of their escape, Twelve and Clara find themselves trapped in an obscure Viking village under siege by an alien impersonation of Odin.

It turns out that this Odin (played by David Schofield with just the slightest wink) leads one of the most feared warrior races in the universe. The village doesn’t stand a chance against the Mire, especially after its own warriors are killed off all at once.

So of course one of the survivors has to go and declare war on them.

Since Maisie Williams was announced as a guest for Series 9, we’ve all been either curious or excited to see how she’d fit in. While I’m not a regular viewer of Game of Thrones, I’m aware of the show, so I know her casting was huge (well, not literally huge). And as the young Ashildr, she well lives up to the hype. It’s no easy task to keep up with Jenna Coleman OR Peter Capaldi, so it says a lot about Williams’s talent and poise that she’s able to keep up with both Coleman AND Capaldi.

Well, now that Ashildr has gone and made the promise, it’s up to Twelve to fulfill it. But he almost doesn’t. It’s just one village this time, not the whole planet, so he’s all too ready to leave them to their fate, until Clara convinces him to listen to that voice reminding him of what he really wants to do. Their confrontation is a powerful scene, at once intense and tender, and would be the high point of any other episode.

But it still gets better. There’s a hilarious training montage (and when’s the last time you saw one of those on Doctor Who?). That doesn’t quite work out, but as Clara promised in that one clip that was all over the internet, Twelve will have a plan. And yes, it’s spectacular. I’ll not spoil it here, but the village’s battle with the Mire is a testament to The Doctor’s way: what you can’t outfight, you can always outthink.

It’s no spoiler that they win. And given the episode’s title, it’s no spoiler that the victory comes at a great cost, to the village and to The Doctor. In another beautiful scene, he wrestles with his guilt and regret, while Clara appears to suggest that all the good he’s done makes up for the loss he’s suffered and caused in its name.

It’s quite the reversal from last season, when Twelve didn’t hesitate to make the bad choices for that greater good, and Clara asked if it was truly worthwhile. But it’s not surprising – throughout Series 9, we’ve seen Clara become more reckless, more careless, possibly more thoughtless. It’s been more subtext in past episodes, but here it’s outright text, and everyone just runs with it.

He’s The Doctor. He can never accept that everyone dies. He can never accept that anyone dies. He has to try to save them. It’s what he does. And in that moment we’ve all been promised, he realizes that it’s why he chose his face.

(The moment when Twelve recognizes a man he once saved in his own reflection lives up to the hype. And it feels like pure Mathieson. He GETS The Doctor. He GETS Capaldi. And he gets that there’s no difference between them.)

Twelve is going to save that girl who died. He doesn’t care how many rules he has to break to do it. And with a lot of help from Mire technology, he succeeds. But as he and Clara leave the village, he still questions himself. That’s also what he does. Ashildr lives. And she’s far more than she used to be. But is she really better?

As Seven once said before, and as Twelve says now, “Time will tell. It always does.”

In fact, it’ll tell next week, when Twelve and Ashildr (or is she?) meet again in “The Woman Who Lived.” And if this part 2 is half as good as its part 1, I’ll be very happy indeed.

So I’ll see you then…

…oh, and since I began with Gally One, I should probably end with it. Meeting Jamie Mathieson was one of the high points of the convention, quite possibly THE high point. He’s funny, he’s gracious, he’s entirely one of us, and the conversation I shared in was genuinely inspirational. I just hope I can live up to his advice…

…OK, now I’m really done this time. Until the next…