A Doctor Who Christmas Special that snatches the sonic screwdriver of success from the shark-jaws of failure. The concept made me groan: do we not all agree that a) the definitive version of Charles Dickens' time travel epic has already been made, and b) that it had Muppets in it? There was no way this was going to be anything but contrived, boring and unnecessary.
Contrived? More than even I imagined. Boring and unnecessary? I was so wrong.
Why does it work? The settings are brilliantly realised, for a start: scenes on the shiny bridge of a crashing starship are ripped from the J.J.Abrams school of sci-fi, complete with lens flare; beneath them, a fog-shrouded semi-steampunk world where schools of fish fly in the clouds.
Secondly, Moffatt's script is definitely one of his better ones, with plenty of twisty timeline changes in addition to the ludicrous and surreal settings he so loves to create. The spaceship is doomed as the local oligarch is the only person with the power to control the planet's atmosphere and let the ship land - but he's a bitter, lonely miser and doesn't care in the slightest whether they live or die. The spark that turns the script from contrived and unnecessary to something more interesting is that the Doctor realises that pleading with the old man won't be enough, he'll have to change his entire history to bring out his better side - and chooses deliberately to play Ghost of Christmas Past to do it.
Kathryn Jenkins is cast as the heroine - whether the part was written for her before or after casting I don't know, but for me no future Christmas will be complete without someone singing beautifully to comfort and calm a dying air-shark. This brings me to the final, obvious point about what is so good about this episode: the shark.