Clara Meets Santa Claus

On a frosty night before Christmas, Clara Oswald is woken up by the sound of something crashing on her rooftop. Putting on her dressing gown, she leaves her room to investigate and is astonished to find Santa Claus, two elves, a sleigh and flying reindeer stranded on her roof. Although she tries to deny Santa's existence as a fairy tale when she is spotted, Santa questions if she still believes in fairy tales, before being interrupted by The Doctor who soon arrives to take Clara away, but not before Santa tells him that he will need his help before the night is over, while offering him a tangerine. After informing Santa that no one loves tangerines, The Doctor follows Clara into the TARDIS. Once inside, he questions her on her belief of Santa, to which she answers that she still does as he whisks her away.

Meanwhile inside a scientific base at the North Pole, a group of scientists make an attempt to save their fellow base personnel, who have been taken over by crab-like creatures. As Shona prepares to enter an infirmary one of the scientist called Ashley tells her not to think about them and to concentrate on something else. Shona enters the infirmary, and begins dancing to Slade's Merry Christmas Everybody which appears to take her mind off the victims. However as she reaches the end of the infirmary The Doctor and Clara arrive on the scene.

As Clara wonders what has happened to the victims, they wake up and begin moving. Shona warns them not to think about what they can see, and The Doctor deduces that the creatures attached to the victim's faces are both deaf and blind, but they use telepathy to keep a constant image of themselves in someone's memory, allowing them to 'see'. As the victims close in, the remaining scientists appear with guns ready to attack, just as several crab-like creatures appear from the ceiling and attack the group.

The Doctor Confronts Santa Claus

Rescue comes in the form of Santa Claus and his two elves. Santa Claus also provides a specimen of one of the creatures which enables The Doctor to identify the creature as a Kantrofarri or a ‘Dream Crab’. The Doctor explains that when a Dream Crab attacks someone, it places them into a telepathically induced dream state. Whilst the victim is 'dreaming', the crab drills into the victim's head and eats away at their brain.

It is during this time that both The Doctor and Clara reveal they had lied to each other during their last meeting; Clara on Danny Pink having returned from the Nethersphere instead of dying while The Doctor falsely claimed to have found Gallifrey. While investigating the Dream Crabs, The Doctor sends Clara to recover Santa's specimen, only for The Doctor to then realise that they use telepathic connections to their intended victims and that if you are thinking about a Dream Crab, a Dream Crab is most likely coming for you. Therefore when Clara enters the room she finds, what was thought was a dead creature, is now missing from the container. It appears and begins to stalk her, at which point Clara tries to distract herself by first thinking of maths equations and then of Danny. This however doesn't work and the Dream Crab attacks her.

The Doctor

Sent into a dream world, Clara is reunited with her dead lover, Danny, on Christmas day but discovers chalkboards with a message warning her that she is in fact dying. However, she ignores them and continues to focus on Danny. The Doctor, needing to save her, allows himself to fall victim to another Dream Crab so as to enter her dream world and confront her. The Doctor urges Clara to believe that it's all just a dream, so they can both wake up. However, Clara does not believe The Doctor, until Danny tells her to accept the reality of his death, stating their reunion has been a bonus for her at Christmas. Accepting this The Doctor and Clara both wake up, discovering that the Dream Crabs die and turn into dust if removed from a host.

But something is wrong. Upon waking back in the research station Clara complains of a pain on the right side of her head. Shona also confirms she has the same pain. The Doctor realises that they have not truly woken up and are simply in a different layer of a multi-faceted dream and have been since the initial attack when they arrived - in reality, none of them actually escaped when the Dream Crabs attacked them. The Doctor proves this with the base's manual, that each of them had been issued with, in which they find that the first word of any chosen page is different for each of them, rather than identical as it should be. The Doctor further deduces that the Dream Crabs could not stop their sub-conscious from fighting back, which came in the form of Santa, who aids them in waking up.

The Doctor decides to leave with Clara, leaving the scientists in their base to deal with the Dream Crabs, but Clara reminds him of meeting Santa on her roof before they arrived and he realises that they are still dreaming from different places and possibly times. On returning to the scientific base The Doctor questions the scientists on why they only have four manuals, when they are a crew of eight people. They then come to the realisation that the victims are really themselves, or rather dream constructs of what's coming to kill them.

Clara

The victims awaken and transport themselves through the bases' CCTV system, killing Albert in the process. The group then travel outside and try to work out a way to escape, which The Doctor suggests using the TARDIS but as they head towards the time-machine, dream constructs of The Doctor and Clara appear. Facing defeat, The Doctor reminds everyone that Santa helped them to survive their previous attack and so tells everybody to use their imagination to dream of Santa. The Doctor, Clara and the three surviving scientists find themselves on Santa's sleigh flying above London.

The Doctor reveals to Clara that the scientists are, in reality, ordinary people and having been rescued by Santa, the memories of the group's real lives start coming back to them as one by one they all wake up in the real world. Until only Clara is left enjoying the sleigh ride.

The Doctor, upon getting free, traces the psychic signal linking their dreams back to Clara and so rushes to her aid and is able to remove the Dream Crab from her face only to then discover that Clara is now an old woman, as sixty-two years have apparently elapsed since they last met. As they catch up together, The Doctor regrets not coming back for her sooner. Their reunion though is suddenly interrupted by the arrival of Santa, who bids The Doctor to act on his regret before it is too late.

The Doctor, realising that he is still dreaming, wakes up for real, and rushes to the real Clara and removes the Dream Crab from her face again. To his relief she is the same age as when he last saw her. Wanting no regrets and offering her all of time and space, The Doctor implores Clara to join him again. As the pair depart, in the TARDIS, they are unaware of a tangerine having been left on Clara's windowsill.