Watch Doctor Who: The End of Time

It's Christmas time again in England, but something is troubling the world's inhabitants. They are all having nightmares about the Master. The Master is a Time Lord who once posed as a human, made himself Prime Minister of England, then proceeded to take over the world with his cyborg army. He was defeated by the Doctor, once again the last Time Lord. While everyone's memories were erased, these visions somehow persist in the present. The Doctor discovers that these visions are not limited to humans, but shared by all the Universe's inhabitants. He also finds out that a piece of the Master survived his death, and his return is imminent.

The Master returns with greater strength, speed, and powers. Once he gains access to an alien medical device, he uses it to transform all of humanity into replicas of himself, much to the Doctor's horror.

This is just the beginning of Earth's ill fate as the other Time Lords, stuck outside of time as a consequence of the Time Wars, are now able to use a recurring thought implanted in the Master's head to escape their prison. They go to Earth and plan on using it as a staging ground to victory in the Time Wars. The Doctor must stop not only his nemesis who controls the planet, but also the Time Lords who threaten the security of the Universe by reviving a deadly intergalactic war.

This two-part episode is notable not only as a season finale, but as an end of a chapter in the revived Doctor Who series. Russell T Davies was the show's primary writer and executive producer since the show's revival in 2005. Doctor Who: The End of Time is notable as his last episode as writer or producer. Additionally, it is David Tennant's last appearance as the Doctor. Previous show writer Steven Moffat took over as executive producer and lead writer after this episode, and Matt Smith played the new Doctor.