Moffat's pastiche of the Star Trek universe - old and new - opens the episode in atypical fashion. The ultra-modern cruise ship on which Amy and Rory are spending their honeymoon is captained by a Janeway clone ("Christmas is cancelled" she decides, after a spot of turbulence) and features a blind navigator who really can't see where he's going despite the whopping great bionic, infra-red whatsit over his right eye ("I'm flying blind" certainly raised a chuckle). Director Toby Haynes also cheekily emulates all those gratuitous J. J. Abrams lens flares into the camera that bedeviled the Star Trek summer blockbuster of 2009.

It deliberately wrongfoots the viewer. For a moment this looks like a tale set most determinedly in the future with Trek-like sleek, anti-septic spaceships crewed by folk running around in crisp white uniforms (very Nerva Beacon for us Ark in Space fans). But mark it as yet another change in attitude from the grungy futurism that Russell T. Davies preferred in his own depiction of science fiction vehicles, bases and technologies. It may well be a parody but perhaps Moffat is now happy to show that a BBC budget can provide more of a Galaxy Quest rather than an Alien when it comes to production design and cash on the screen.

Whatever your thoughts, the visual dichotomy is established from the opening. Sleek futurism is contrasted with the faux Victoriana of Sardicktown and it must be said that you couldn't have asked for better from production designer Michael Pickwoad's debut on the series. It's a very handsome, often gloriously sumptuous looking episode with Pickwoad not only facilitating a fusion of Dickens and Metropolis in his work on Sardicktown but also adding in some Verne like modifications to the TARDIS. The rather angular looking railings that run up the steps and around the console have been replaced with more suitable curved, brass versions. The nod to Verne is carried through into the interiors for Sardick's home, the environs of the town, most definitely more 'Nautlius' than 'Noel' with the dominance of great porthole like circular windows, vast chambers and basements and the riveted coffin-like suspended animation pods all echoing Disney's classic version of 20,000 Leagues Under the Sea and more recent fare such as The Golden Compass.

For those that may have joined the party late, the pre-titles more or less sums up the story so far. Mr and Mrs Pond are on honeymoon, and clearly indulging in some cos-play in the privacy of their own suite (the policewoman and the Roman centurion echoing all the way back to The Eleventh Hour and The Pandorica Opens and that photo that River found in Amy's abandoned house) and the Doctor, as ever, is lacking in punctuality as they wait for his response to their distress call. 'Come along Pond' flashes up on the viewscreen to mark his late arrival and Amy, in repudiation of the Janeway-like Captain's earlier humbuggery towards the festivities, believes Santa's back in town when the TARDIS swoops overhead and she knowingly declares, in reflection of the episode's own explicit mission statement, "It's Christmas."

Lovely to see Arthur Darvill's name in the opening titles at last and I'm not sure if my ears deceived me but was there a bit more oomph in those crashes of lighting striking the TARDIS? As the Mill's CGI gives way to a plunge (rather Citizen Kane-like) through the girders and construction of Sardicktown and settles in the bustling streets, Moffat immediately makes a connection with us, here and now in post-Coalition government Britain, briefly reminding us with the newspaper headline 'Spending Plummets, Tax Soars' that his revisiting of Dicken's own Carol is as much about the haves and the have-nots of Cameron and Clegg's Britain as it is about Ebenezer Sardick's cruelty and soullessness.

If anything, I would see A Christmas Carol as a further development of the political satire of his episode The Beast Below with its own thinly veiled satire on the May election. Gambon's syrupy reflection on a populace relieved to have emerged from the darkness of Winter and anticipating the coming of longer, brighter days, marked by the Christmas festivities and the solstice, is wonderfully turned into the bitter rant of "you know what I'd call it? I call it expecting something for nothing!" that is just as chilling as recent attacks on public spending.

Dickens was, for all intents, a political writer and Moffat's choice to 'borrow' the story of A Christmas Carol for his own purposes does not strike me as unusual in the least.  Series 5 is suffused with many of these views, is clearly a specifically authored text, and there was little doubt in my mind he would stop here, despite what would be an obvious use of political and cultural analogies in the Dickens story to our own, all too cold, harsh reality. What impresses me most about Dickens’ work is how relevant it is to our own times. Scrooge and Sardick are fiscal conservatives, statesmen dealing with the realities of their situation. Sardick even has the President's ear and his control over the skies of his own world allows him to deny a request from the President to allow the ship carrying our honeymooners and 4,000 other souls to land. When Sardick remonstrates with the President about giving the ship clearance to land with "we already have a surplus population. No more people allowed on this planet" it correlates to Scrooge's own view of the poor who claim they would rather die than go to the workhouse. Scrooge suggests they continue with their demise and "decrease the surplus population".

Gambon is perfect casting for the story's antagonist. In Moffat's eyes, he isn't the villain, he's actually a victim. But it is only through the agency of the Doctor that we see him as a victim. Gambon gets some deliciously horrible things to do and say to the poor family begging to see their frozen sister for just one Christmas (poor families take out loans from Sardick and the guarantee on paying him back is to freeze a member of their family - again, as per Scrooge's suggestion, reducing the population) and I was reminded of his turn as the foul-mouthed Albert Spica in Greenaway's The Cook, the Thief, His Wife & Her Lover and of the victimhood of Philip Marlowe in Potter's The Singing Detective. He's a pleasure to watch in this and he has complete mastery over the character, able to convince us that Sardick is simply misunderstood and has very good reasons not to be cheerful.

When he demands that the poor family go home and pray for a miracle (religious themes and symbolism are again front and centre here - from the fish that thrive in the crystalline atmosphere of the planet to the human lives bought with the currency of Gideons - and the Doctor as a miraculous and God-like presence is an oft used theme in the series. Popping out of the chimney Moffat equates him with Santa and even uses him to convince a disbelieving young urchin that Santa does exists and that "he should keep the faith and stay off the naughty list."  As the Doctor attempts to use Sardick's cloud control machine there's a lovely in-joke about isomorphic controls (a little bit of classic series continuity that was always rather dubiously and quickly ignored) when the Doctor claims to Sardick that "there's no such thing" as isomorphic controls and then is proved wrong in a pleasing moment of physical comedy between the two actors.

A physical act is the turning point of the story. When Sardick reaches out to strike the young boy who hits him with a piece of coal and he freezes, unable to continue with such an act of cruelty, the Doctor determines a weak spot in the man's armour. It is the slenderest of moments on which to hang a plot that sees the Doctor deliberately going back into one person's time stream and affecting a complete change in their personal history. One could argue that if the Doctor can easily pop in and out of anyone's time stream and change them and their history it suggests the whole 'fixed point in time' business that the series has been banging on about is nothing but a fallacy and that the Doctor could simply go back in time and rescue the crew and passengers of the ship rather than loiter around in Sardick's closet full of skeletons.

And clearly cries of 'whatever happened to the Blinovitch Limitation Effect?' can be heard from the backbenches of fandom at the sight of young and old Sardick crying into each other's finely tailored Victorian coats come the conclusion. The idea of changing history and interfering with time doesn't seem to follow any of the previously laid down rules when we look at what Moffat engineers in A Christmas Carol. Even though the Doctor takes Sardick back into his own past, shows him his present and gets his younger past self to confront his older future, the Sardick family still holds sway over the skies and the achilles heel in Sardick's behaviour merely changes from one of psychological damage inflicted by an overbearing, violent father to one where he simply has a broken heart.

The Doctor deducts that it is daddy Sardick who has caused this self-hating people abuser to persist in his curmudgeonliness and Toby Haynes uses a succession of zooms and cuts on faces, chairs and portraits to summarise this process, reflecting the way the Doctor always spots the detail in his immediate surroundings that was first demonstrated to us in The Eleventh Hour. "You're scared of him and you're scared of being like him," concludes the Doctor but he believes that Sardick is a particular case that can be cured because he couldn't actually bring himself to hit the boy. It's the Doctor's gift to him, signed off with "Merry Christmas, Mr. Sardick." As is suggested by the Doctor, Sardick is now "half way out of the dark", as Christmas is the turning point of the year and the world emerges from the dark into the light. This is symbolically depicted in the Sardick corporate branding of the spiral S shape that has more than a passing resemblance to the yin and yang symbol. Thus the story becomes a dance between the polar opposites, between the contrary forces that give rise to each other - dark and light (the gloom of Sardicktown and the bright white of the ship), male and female (Sardick and Abigail's relationship, the younger and older Sardick, the Doctor and Sardick as visual analogues to each other), life and death (Abigail as the Sleeping Beauty or Snow White fairy tale figure doomed to die to give Sardick life again), predator and prey (the shark and the fish, the Doctor and Sardick).

The fish and the sharks living in the cloud layers are a wonderfully bonkers idea. The marauding sharks are apparently one of the younger Moffat's fears as a child, probably generated from watching Jaws far too many times. Clearly, the shark is a emblem of authority and aggression but it is also rather an apposite choice to represent Sardick himself, as the dark shadow swimming the skies of this world and his nature problematised by his response to parental abuse. Sometimes this type of shadow is represented in fairy tales as the dragon guarding the treasure, the being that looks fearsome and frightening but who is, in fact, only there to keep something priceless from harm until it can be claimed by its owner or someone willing to confront the beast within. Here it is Sardick reconciling his fears of his own father and coming to terms with his relationship with Abigail. The imagery here is fantastical, perhaps one of Moffat's most charming visual metaphors and one that bends the rationality of the story, turning it into a dream-like odyssey that, along with the Victoriana and the chimney sweep like Doctor figure, reminded me of Kingsley's The Water Babies.

The shark will no doubt have many reaching for the obvious accusation that the series has indeed, literally, jumped the shark. I don't think that's the case here at all. There is the troubling nature of the Doctor's eagerness to rewrite someone's personal history and how the consequences of his actions will reverberate through causality. All of it just to get an old mardy-pants to be nice for a bit but only for him to muck it up by instead committing them to a doomed love affair when we discover Abigail, the object of Sardick's affection, can only live for 8 days. Despite this, the story is solid entertainment, with Moffat managing to include his customary motifs of mind-scrambling past, present and future sub-plots, with a sense of the cubist drama I talked about in my book which Toby Haynes latches onto with his impressive ability to visually represent Moffat's compression of time. 

There is the weird Peeping Tom like moment where the Doctor shows the older Kazran home videos of his younger self (and he learns life's most invaluable lesson - that "nobody comes" when you need them - and thus emphasises his abandonment issues) and the Doctor actually steps into the projected image to become part of it as he enters through the boy's bedroom window (Peter Pan metaphors again) and begins to change the boy's life and immediately give the older Kazran a new set of memories. There is talk of Face Spiders that live down the back of wardrobes (I want an episode featuring them now, Mr. Moffat) and an amusing gag about the psychic paper failing to offer the Doctor's credentials as a babysitter ("a lie too big" for it to cope with) as once again the Doctor takes a child out into the foggy night, just as he did with Amy, to fly above the city and to catch the biggest of fishes ("because they're scary" and represent our inner fears).

The cubist nature of time is perhaps nowhere better seen in the sudden switch between the older Sardick watching his younger self and the Doctor on screen. As they attempt to open the vault containing the 'surplus population', they demand the necessary combination. Like someone in a pantomime audience the older man shouts out the combination, at first unheard because he's simply shouting at an image, but then is acknowledged by the Doctor who has instantly slipped forward in the TARDIS to get the combination from the older man. It's a lovely, playful visual and narrative moment.

Laurence Belcher is quite superb as the younger Kazran and the whole sequence of him and the Doctor encountering the shark, meeting with Abigail and flying over the city is pure fairy tale, evoking the likes of Mary Poppins and Bedknobs and Broomsticks. The visual effects sequences by the Mill, and featuring the shark and the flight over the city, are perhaps some of the best ever featured in Doctor Who. Magical and Christmassy. We also see Moffat's manipulation of time later in the charming sequence of various Christmas Eves where the Doctor and Sardick repeatedly defrost Abigail (confronting her with a maturing Kazran, a variety of headgear and trips to Abigail's family, travels all over the world and a visit to Hollywood in the 1950s). What really shouldn't work is the notion of Katherine Jenkins singing to a shark. I mean, it is utterly ridiculous, isn't it? Completely daft. But somehow, in some strange way, the fantasy of it becomes transcendent (where the impossible doesn't happen "except at Christmas" argues the Doctor) and the sequence where she sings 'In the Bleak Midwinter' to the beast is curiously very affecting.

Later, after the romance has developed between Kazran and Abigail ("it's this or go to your room and design a new kind of screwdriver. Don't make my mistakes" advises the Doctor to the young man, once again emphasising his own state of innocence about these matters) the Doctor hopes the memories of it will change the older man. Little does he know that a broken heart and loneliness is as much to blame for the older Kazran's disappointment with the world as is a domineering and violent father. As the older Kazran states, learning from the Doctor, "life isn't fair". When confronted by the doomed passengers on the ship and the holographic Amy, he refutes her claim that "time can be rewritten" by arguing that people certainly cannot and that the Doctor's interference in his life has simply underlined his hard heartedness rather than change it. Gambon is very affecting here especially when the Doctor reasons, "Better a broken heart than no heart at all" and Kazran snaps in reply, "Try it! You try!" and is as angry as anyone would be that the Doctor has simply swapped his one tragedy for another.

Only when Kazran is confronted by his younger self, brought to the future by the Doctor to witness his older self's bile ("I don't and never, ever, will care!"), does his role switch to one of the default hostile father threatening to beat his younger self and finally forcing his folly into perspective for him. Only then does he feel regret and understand that the interchangeability of nature (‘The man is father to the child. The child is father to the man', as Gerard Manley Hopkins wrote) provides him with his mistakes. But the Doctor has changed him so much that he no longer has control over the cloud controlling machine and only Abigail's voice can calm the storm. It's a nice way to integrate Jenkins's singing into the story and she sings 'Abigail's Song' beautifully, perhaps one of Murray Gold's finest contributions to the show.

It is again very moving just when it should plainly be rather risible (I'm sure we all wondered just how Katherine Jenkins's singing would be relevant to the plot) and the scene is carried superbly by Gambon and Jenkins. It is heartfelt and full of melancholy, precisely 'half way out of the dark' as the episode requires. Jenkins doesn't embarrass herself at all and Abigail's demise is aptly tragic and even the lyrical refrain of 'let in the shadow' perfectly summarises how Kazran must reconcile his darker self and accept "their last day together" where the Doctor also recognises the integration of the yin and yang in "everything has got to end sometime otherwise nothing would ever get started". Perhaps it is even a note of prophecy on Moffat's part when you consider some of the eyebrow raising images in the trailer that followed.

In conclusion this is a different, almost introspective Christmas special where a sense of the epic is merely the background to a personal story about one man's relationship to his father and where even the gifts offered by the Father Christmas of time and space can bring their own disappointments and consequences.