So at the end of it all, “Turn Left” is pretty clearly the first fifty minutes of a three-hour epic. Though that wasn’t obvious at the time, now there should be no question. Thing is, it serves not only as the setup for Donna’s character arc; in story terms it serves to set up both the nature and the significance of the events to follow over the next 115 minutes. Without it, the final two episodes are just so much aimless bluster.

There’s all the foreshadowing of the supporting cast’s fates, were Donna not involved. Rose’s story is a straight through-line — she spends “Turn Left” righting events so she can get straight to work on the timeline in “The Stolen Earth”. They’ve all gone wrong because Donna wasn’t there to help. Heck, Rose tells her right off that she’s going to die — and that she isn’t talking about in the alternate world (where she is incidentally going to die, however). She means the version of her who travels with the Doctor — as becomes more clear in retrospect, especially with Donna’s meltdown about how she can’t die, because she was going to travel with the Doctor forever.

Ultimately, the biggest reason to connect it is that it gives us a starting place. It shows us who Donna was, and why she was as she was; how little support she got from anyone, least of all Sylvia. And then, the story comes full circle. In the first fifty minutes we saw what she might have been, what she was capable of even if she had never met the Doctor, if only someone had believed in her. Then she’s returned to that situation, and Sylvia is given a second chance to do right by her.

The point of the story is basically that the proposal in “Turn Left” is fulfilled. The Donna whom we leave is a Donna who has in effect turned right. Yet the distinction has been pointed out to all concerned parties. The Doctor put a big bullet point on it. If you think she was better with me, he tells Sylvia, then take care of her, dammit. That’s just who she is, if you’ll allow it. And for such an immense story to basically be about that… As a writer Davies really hammers on this issue of faith, doesn’t he. Though it’s always humanist; about how you treat others.

It’s just so much better and more complete a story, when you take it in full. Even the pacing makes more sense that way, with it getting more and more frenetic as it builds, keeping up the tension, keeping things from seeming like they’re dragging after you’ve been sitting there for a couple of hours already.

As a three-parter, I’ve got to say it has to be the most incredible epic the show has ever attempted — just on an emotional level, never mind the spectacle and sinks (and plungers). The scope is nothing to sniff at, of course. Yet without that episode… it’s just so much wank. There’s no anchor. It all seems so much smaller and more confused.