Twelve Nights

Twelve Nights was a special Christmas series of Doctor Who starring Peter Capaldi as the Twelfth Doctor. It aired in 6 episodes, with the finale airing on Christmas Day. Each episode was named after a notable Christmas songs.

Story
It follows The Doctor returning to the town of Christmas on the planet Trenzalore long after his last visit. The people of Christmas tell The Doctor that an urban legend locally is that upon the return of The Doctor, Christmas would finally find peace and return to the traditional seasonal cycle, defeating The Snow King that rules over the town from the clouds.

Episode 1 - I Wish It Could Be Christmas Everyday
The Doctor is called back to Christmas, Trenzalore 4 million years after his last visit. The locals believe he is their only hope in defeating the evil Snow King who rules from the sky above. The Doctor has twelve nights before the town of Christmas loses it's seasonal cycle and it's people cease to exist as they do today.

Episode 2 - Do They Know It's Christmas?
The Doctor is offered lodgings by a family living in the heart of Christmas, the youngest member - a girl named Jayney tells The Doctor there is only one way to reach The Snow King and it's to climb to the top of The Ancient Clock Tower and freeze the clock, but she adds that anyone who has ever tried has not lived to tell the tale. Will The Doctor take the risk to save the people who once worshipped him?

Meanwhile, The young people of Christmas are enthralled by the TARDIS and get lost within it's corridors, can they find their way out before the exits are deleted?

Episode 3 - A Winter's Tale
The children of Christmas accidentally take the TARDIS far into the future of Christmas and make a horrific discovery.

Meanwhile, The Doctor gathers the town people to prepare for his confrontation with the Snow King, but he learns that he isn't the only threat facing Christmas - Missy has arrived.

Episode 4 - Christmas Wrapping
Missy has declared herself Queen of Christmas and reveals to The Doctor she has come in peace. With Yule Day quickly approaching, The Doctor promptly encourages the Christmas people to prepare with gifts and other Yuletide activities. In private, Missy reveals the true reason she has arrived at Christmas. She knows the identity of the Snow King, teasing The Doctor she refuses to reveal his name.

The children of Christmas beg the TARDIS to take them home, with no hope of learning to fly the time machine, the six youths try to evade the monster that lurks in futuristic Christmas.

Episode 5 - Merry Xmas Everybody
The Doctor and Missy build the perfect contraption to trap the Snow King, but as the weather worsens in Christmas, the citizens take it as a warning from the Snow King and warn The Doctor to leave him be, which amuses Missy.

The six children defeat the monster and it's dying moments it tells them they're not in Christmas, but are in fact in the neighbouring town of Easter. He laughs as the TARDIS disappears without them. Trapped, the youths decide to try and return to Christmas and find refuge there until they can attempt to contact The Doctor in the past.

The contraption is complete and it's time for Missy and The Doctor to head up into the sky, Jayney insists on accompanying them. Missy tells The Doctor that he should know who The Snow King is before knocking on his palace door, when The Doctor asks who it is, Missy replies with one word, "You."

Episode 6 - All I Want For Christmas
Jayney, Missy and The Doctor arrive at the doors of The Snow Palace, a baffled Doctor continues to question a giddy Missy who explains that The Doctor left behind a jar of Atron Energy upon his regeneration and someone had released it, creating a new incarnation of the Time Lord. Missy turns around and points to a tearful Jayney, who confesses to the mishap. She tells the duo about how she had found the jar in the Clock Tower where The Doctor had died previously and believing it to be fireflies, she released them into the air. As the energy flew away, it mixed with the flurries of snow and formed a Time Lord/Snow hybrid. To seek revenge for his bad treatment within the jar for millions of years, The Snow King inflicted terror through weather on the town of Christmas.

They burst into the palace and confront the entity, a ruthless Doctor tells it that there's only room for one Doctor in the town of Christmas and destroys it. Trapping it's Atron Energy in a ziplock bag. He tells Jayney to protect the bag with her life and never open it. Jayney nods and places it in her satchel. The trio return to Christmas, which has become a lush green since they departed. The people thank him and he returns to the TARDIS.

A trio of mothers burst through the crowds and beg The Doctor for help. Their children are missing. The TARDIS lights up and The Doctor smiles. He tells them he will return shortly.

Travelling years into the future, to the top of the clock tower - The Doctor finds the six children sleeping peacefully. He wakes them and they grin gleefully. He takes them back to their rightful home to their mothers' relief. Jayney comes forward and asks The Doctor if he's happy travelling alone, to which he replies No. Jayney offers to keep him company as a companion, The Doctor agrees.

As they say their final farewells, the town declares Missy as their Queen, to her joy. The Doctor wishes her the best, knowing this isn't the last he's seen of her. The Doctor takes Jayney's suitcase and promises her family she'll be fine and thanks them for the hospitality. The TARDIS fades away and leaves a view of endless green hills behind it.

Peter Capaldi as The Doctor
An eccentric and wise Time Lord who was once considered a God by the people of Christmas - he returns to help them with their problem.

Michelle Gomez as Missy
A quirky and mischievous Time Lady and frenemy of The Doctor. She arrives in Christmas to warn The Doctor.

Raffey Cassidy as Jayney
A young girl from Christmas who takes an interest in The Doctor's behaviour after he takes up lodging in her family home. She becomes The Doctor's companion at the end of the series.

Matt Smith as The Snow King (Voice)
The Snow King is a weather entity that lives in the snow clouds above Christmas, he originates from a time when abandoned Atron Energy mixed with snow. His mistreatment in the jar led to his evil tendencies of torture via weather in Christmas.

Behind the Scenes
Michelle Gomez's return was kept top secret until broadcast.

Matt Smith's appearance was included as Steven Moffat, the writer, wanted to show that he was the product of that Doctor's incarnation's regeneration.

Christmas last appeared in The Time of The Doctor, Matt Smith's last regular appearance in the show.

Due to Raffey Cassidy's age, she will remain a recurring character in the next series, but her absences will be addressed.