"There are also elements from every series of Matt's Doctor, which will come to a head in this special. Things that we've laid down for years are going to be paid off," says producer-writer Steven Moffat.
Back on Earth though, the Doctor must first face other stresses - like helping Clara (Jenna Coleman) cook a family Christmas dinner.
Despite it marking his goodbye and a final battle, Smith describes the episode as feeling "wonderfully Christmassy".
"The Christmas special for me is a bittersweet episode because I'm leaving, but Steven has written a brilliant, adventurous, funny episode and I'm really thrilled with it.
"I think it's good for the Doctor to go out with a bang, a crash and a wallop. I'm pleased it's really funny and mad. When I got to the last 20 pages it was quite a hard read for me, but I hope it's going to be a belter."
Moffat says it wasn't a deliberate move to cast an older actor as a replacement to Smith, the youngest actor to hold the role. The 55-year-old Capaldi was just too good an idea.
"It wasn't the reason I cast Peter, but I do think if we'd cast another Doctor as young as Matt - because Matt's been so good at being the Young Doctor - I'm not sure what another one would have done. They'd have to have either been deliberately different or just repeat him."
Coleman, who will now become assistant to Capaldi in future episodes, told TimeOut last month filming Smith's final scenes had been an emotional experience.
"The entire episode was. I knew it was going to be very hard to see him go ... I think it took us both by surprise how emotional the episode is.
"It feels like the Doctor and Clara have just got into this place enjoying their adventures together, and it's almost that it's been cut too short in a way. It's kind of what makes it beautiful as well."
Comedy pick: Mr Stink
Based on British actor David Walliams' best-selling book of the same name, this star-studded BBC special has plenty to offer adults and children alike. Hugh Bonneville plays the title character - a homeless man who hides in a shed in young Chloe's garden when he's worried he might be driven out of town with his equally stinky dog, Duchess.
Walliams plays the Prime Minister, with little time for the plight of the homeless. As Chloe struggles to make sure no one sniffs out Mr Stink, she also has to cope with an overbearing mum who is more interested in her own political ambitions than her daughter, her put-upon dad who has a secret of his own, her perfect younger sister Annabelle and the nasty girls at school.
And then it turns out there might be more to Mr Stink than meets the eye - or nose.
When: Tuesday, 7pm
Where: UKTV
What: Heart-warming British romp
Music pick: Lady Gaga and The Muppets' Holiday Spectacular
Lady Gaga may not traditionally seem like a kids' entertainer, but the Muppets turn out to be the perfect funny, furry foil to Gaga's nutty avant-garde songs and costumes. The star bonds with the Muppets cast, sharing the difficulties of life on the road, and explaining how she grew up watching the Muppets and her long love for Kermit (he was her date to the 2009 MTV Awards), in between performing a variety of hits from her latest album,
Artpop
, and some holiday favourites.
Elton John is on hand to perform the title track with her (facing each other across two grand pianos) as well as Bennie and the Jets, and Joseph Gordon-Levitt shows off his vocal skills in a duet, too. Lady Gaga's costumes are as elaborate as ever, but her banter with the Muppets is warm and endearing, particularly when singing with Kermit.
When: Sunday, 7pm
Where: TV2
What: Colourful pop bonanza
Variety pick: Royal Variety Performance
The stars and royals - Prince Charles and the Duchess of Cornwall - gathered for the 101st Royal Variety Performance at London Palladium last week, and were treated to another whirlwind show in the name of charity. Now viewers at home can look forward to enjoying the show on Christmas Day.
Liverpudlian comedian and Graham Norton regular John Bishop is the host, introducing a huge array of singers, including Gary Barlow, Robbie Williams and Olly Murs, Jessie J, Mary J. Blige, rising star John Newman and Bryn Terfel.
Dame Edna Everage pops in with a wink or two, legendary figure skaters Torvill and Dean pop on some roller blades to take to the stage, and the cast of a new show, I Can't Sing! The X Factor Musical, provide a highlight, with some very funny lyrics indeed.
When: Wednesday, 7.30pm
Where: TV One
What: You never know what will be next
Drama pick: The Bible
Anyone thinking there's not enough religion on the telly at Christmas may have to think again. The greatest hits of both Testaments are stretched over five 90-minute episodes in this miniseries from producer Mark Burnett, one of the big names of American reality TV with shows such as
Survivor
and
The Voice
.
When the show screened on the History Channel in the US in the lead-up to Easter this year, it set viewership records for a cable TV series. Each episode has two or three better-known Bible stories, told with a mix of live action and computer generated-imagery, helping to create those miracle moments such as Moses parting the Red Sea. It features an international cast of unknowns, including Portuguese actor Diogo Morgado as Jesus and Burnett's wife and series co-producer Roma Downey as his mum, Mary.
When: Monday, 8.30pm
Where: Vibe
What: The good book adapted for TV
- TimeOut
