Christmas Day will see thousands of families gathering on the couch in front of the television in the evening for the eagerly anticipated new episode of 'Doctor Who'. The Doctor is struggling to come to terms with the death of Clara, but his wife seriously needs his help.

Alex Kingston and Peter Capaldi in Doctor WhoHusband and wife are reunited in the first look at the 2015 Doctor Who Christmas special

Yes, the December 25th episode brings with it a lot of twists and turns and some thrilling guest appearances. Here's what we know so far about the show:

1. River Song will return, and it will be the first time Peter Capaldi's twelfth Doctor meets her. The character, played by Alex Kingston, was last seen in 2013 episode 'The Name of the Doctor'. It was an emotional farewell between them, but we always knew it would only be a matter of time before they saw each other again - and if there's one thing these guys have got enough of, it's time.

2. Clara Oswald will not be returning as the Doctor's companion. She met an untimely end, just as her lover Danny Pink had done in previous seasons, in 'Face The Raven' which means there's a new vacancy in the TARDIS. However, it's unlikely we'll meet the new companion in the Christmas special, as Steven Moffat wants to give fans a mourning period.

More: Peter Capaldi won't confirm or deny possibility of Maisie Williams as new companion

3. Matt Lucas and Greg Davies will make guest appearances which can only be a good thing. The Christmas special promises a lot of laughs with the likes of these TV stars, who play characters named Nardole and King Hydroflax respectively. We know that Hydroflux is angry about something, his Robot guard is on the rampage, and Nardole's survival is in question.

4. It will be a fast-paced episode filled with imminent danger and cosmic pursuits. A miserable Doctor attempts to spend Christmas alone, away from the revelry and festivities, but it isn't long before he is forced to accompany River Song on a perilous new adventure.

5. It won't be Christmassy. While last year's episode featured a sleigh ride with Santa, there won't be as much mistletoe and wine in the upcoming special. This is all about River and the Doctor re-connecting.

6. It is directed by Douglas Mackinnon, who was also at the helm of the upcoming 'Sherlock' New Year special 'The Abominable Bride'. It will mark his eighth venture in the time-travelling series, his last being 2014 episode 'Flatline'.