Written by Steven Moffat, this episode serves as both a Christmas special and a regeneration story, sending off Matt Smith’s Eleventh Doctor after four years. It directly resolves the "Silence Will Fall" / "Doctor Who?" arc introduced in 2011’s "The Impossible Astronaut," and brings back Clara (Jenna Coleman) as the companion.
The Doctor is summoned to the planet Trenzalore, where a mysterious signal—later revealed to be a question asking his real name—emanates from a crack in time. The answer would either unleash the Time Lords (trapped in a pocket universe) or restart the Time War. The Doctor stays to protect the town of Christmas for hundreds of years, aging drastically, until the Time Lords grant him a new regeneration cycle. Doctor Who 2005 2013 Christmas Special The Time...
If so, here’s a concise review of that Christmas Special: Written by Steven Moffat, this episode serves as