WARNING: THERE ARE SPOILERS IN THIS REVIEW, AND LOTS OF THEM. DON'T READ IT UNTIL YOU'VE SEEN THE EPISODE!

To this day, I sit here wondering if the finest casting decision that Russell T Davies oversaw during his tenure on Doctor Who – outside of his title stars – was the appointment of Bernard Cribbins. At times, when the generally very good The End Of Time Part One was threatening to lull a little, Cribbin’s Wilf not only steadied the ship, but also gave the episode its finest moment. The still scene in the café when, with tears forming in his eyes he practically begged The Doctor to help Donna was exceptional. Tennant was wonderfully restrained, and Bernard Cribbins was simply superb. He’s created a  moving, believable character, who seems to be at the heart of the coincidences that set up the story.

And it was a surprisingly dark tale we got for a Christmas Doctor Who episode, too (even factoring in the regular deaths in Voyage Of The Damned). That’s appreciating that we all know where this tale is heading, but even so, there was little concession in tone to the festive season. The foreboding voiceover at the start quickly brought the image of The Master into things, as if Russell T Davies was very keen to get down to business quickly. But even the post-credits first scene, where Tennant steps out of the Tardis in his holiday gear, is quickly quashed with the appearance of Ood Sigma standing in the snow. There’s no time for pratting around at all.

We’d already seen this scene, of course, when the BBC showed it during its Children In Need telethon, and in hindsight, it gets through a lot of work. Not only is everyone having dreams, not only is The Master coming, but there’s something bigger instead. What’s the something bigger? Mr Davies is understandably holding the full scope of that and a few other cards back for New Year’s Day, but things are set up quickly and efficiently here, and a lot happens in an hour.

There’s the resurrection of The Master for starters, but it’s here for this reviewer where the episode suffered the most. The bringing back to life of one of the Doctor’s deadliest enemies I thought was bordering on the wrong side of ludicrous, and it really offered a taste of what was to come for the character. It was loud, daft and over the top: themes we’ll be returning to later. It’s a shame that Alexandra Moen’s Lucy Saxon didn’t get much to do here, but the character was here to serve a narrative purpose, before going kaboom. On the plus side of the Master’s regeneration, at least it was done very quickly. A wise choice, given that it was all just a little bit silly.

Not as silly though as The Master’s subsequent transformation into an auditionee for Ang Lee’s Hulk movie. The Master jumping high into the air? That was just outright daft, and for me went against what makes him such a potent foe for the Doctor.

I’ve always loved The Master as an enemy, as he’s the one foe the Doctor faces who’s the most obvious foil for him. It’s two equals, going head to head.When you then give The Master superpowers, where he can leap over high buildings and fire bolts from his hands, you disturb the balance and make the fight a little less interesting as a consequence. That may just be me, granted, but I thought that the elements surrounding The Master were the weakest parts of The End Of Time Part One (although, to be fair, he was bonkers enough to be unsettling).

Still, they were the weakest parts of an episode I still thought was very good. Clearly much of the time was spent sliding pieces around the board, preparing us for what’s around the corner. We know, for instance, that Joshua Naismith is both rich and stupid, clawing back old Torchwood technology that may as well come with a warning notice that if you use it, you’ll screw up the world. His driving force is, apparently, immortality for his daughter. We’d wager a bit of cash, therefore, that she’ll be dead by the time the credits roll on New Year’s Day.

There were also characters brought in whose main role in the story is yet to be determined. The two cactus people – I’m not even going to attempt to spell their real name – clearly are potential allies for the next episode, and the fleeting glimpse of Timothy Dalton in Time Lord gear is arguably the most exciting little taster for what lies ahead (we didn't get the full end of episode scene with the Time Lords at the preview screening, but that end sequence of the episode we've since caught up with was terrific). The glimpse that we got sent my my geekbumps went into overdrive. The Time Lords are coming (in fact, there are billions of them technically by the end of the episode).

But perhaps the most interesting piece of the jigsaw is Donna. For the first half of the episode, she was in exactly the state she was in when we left her. Back to her usual catchphrase spouting self, oblivious to the events that led her to become the Doctor Donna.

Yet there was something more, and the first clue we got (and, to be fair, we didn’t assume that Catherine Tate had been brought back just to make up the numbers) was when she bought her Grandfather Mr Naismith’s book for Christmas. But more was to come. And her importance to the events of Doctor Who was confirmed though when the only person on the planet to not be affected by The Master’s mind-warping plan – which even took out Barack Obama (or, let’s charitably say a vaguely convincing lookalike of him) – was Donna. Wilf was exempt because he just happened to be in the chamber with radiation sealing (from the moment you saw said cabinet, you figured it had to be a plot get-out-of-jail card somehow). Donna? She’s the only person on the planet, the Doctor aside, who actually resisted it herself.

Why is that? Is that her being half-Time Lord? Whatever the explanation, she’s going to be pivotal to Part Two, clearly, which is where several other familiar faces are going to be returning.

Finally, then, there was the cliffhanger with the multiple Masters. And this, again, was daft, although I suspect it's a crowd-splitter. I can see that argument that it matches the scale of the story, for instance.

Anyway, I’ve always argued that Russell T Davies writes great cliffhangers and strong penultimate episodes. This, for me, wasn’t one of his best endings. The idea of turning pretty much everybody in the world into The Master was again just, well, a bit silly. It was entirely in keeping with the decision to turn the batshit-crazy meter on The Master through the roof, and John Simm was clearly having a ball (and testing the BBC’s wardrobe deparment to the limit). But all of a sudden it’s transformed what could have been a fascinating one vs one battle between the Doctor and The Master into a one vs eight billion. I suspect Davies has a masterplan for this, and that he’ll pull it out of the bag. But on paper at least, it makes for a less interesting fight right now.

That said, and I appreciate I may have come across over-critical here (although, in my defence, this two-parter has been top of to-watch wishlist for a long time now, so my hopes and expectations aren't low), I still thought The End Of Time Part One was very good. It managed a delicate balance between delivering a Christmas episode that the family could enjoy, and putting into place some fairly dark stepping stones for the journey ahead. That’s really no small feat when you reflect on it. And behind the camera, Euros Lyn deserves credit for his fast, flowing direction, while keeping things still when required too so that Bernard Cribbins’ eyes alone could bring a lump to the throat.

It’s clear, however you felt that the cliffhanger went, that the second part of this adventure is set to be epic Doctor Who one way or another. There’s a near feature-film length running time, a big cast and no need to pull back on the ending and save everyone this time round.

It presents a different challenge, of course, in that we know where Davies must leave the show by 9pm next Friday. But freed from both the demands of a Christmas episode, and with the world and time itself facing disaster, the blocks are now firmly in place for what could and should be a dark, enthralling final episode.

It might be an idea to put The Master on a bit of a leash, though…