The BBC has released an official plot synopsis for the forthcoming Christmas special of Doctor Who.

The episode, which is titled 'The Time Of The Doctor', will see Matt Smith make his final appearance as the Time Lord before he is replaced by The Thick Of It actor Peter Capaldi, who will take over the role at Christmas and then go on to star in his first full series in 2014.

The BBC's official synopsis says: "Orbiting a quiet backwater planet, the massed forces of the universe's deadliest species gather, drawn to a mysterious message that echoes out to the stars. And amongst them - the Doctor.

"Rescuing Clara from a family Christmas dinner, the Time Lord and his best friend must learn what this enigmatic signal means for his own fate and that of the universe." You can see a trailer for the episode by clicking at the bottom of the page.

The Doctor Who 50th anniversary special 'The Day Of The Doctor' was broadcast last week (November 21) and was watched by 10.61 million viewers at its peak, averaging 10.2 million viewers throughout. The show's current stars, Smith and Jenna-Louise Coleman, were joined for the episode by popular former Time Lord David Tennant and companion Billie Piper, as well as by John Hurt.

'The Day Of The Doctor' was simultaneously shown on BBC and in 3D in over 200 UK cinemas, as well as in cinemas in the US, Canada, Germany and Russia.