Jamie: Have you thought up some clever plan, Doctor?The Doctor visits Tibet in 1935 in order to return a sacred bell he was given last time he was there. He meets Travers, an English explorer trying to track down the mysterious Yeti, and the High Lama Padmasambhava, who has miraculously remained alive since the Doctor's last visit hundreds of years earlier.It transpires that an alien creature — the Great Intelligence — has taken over Padmasambhava, prolonging his life, and that the Yeti seen in the area are robots, there to scare off or kill inquisitive travellers. The Great Intelligence is a non-corporeal creature (who previously met the Eleventh Doctor) trying to create a form for itself in order to take over the Earth. The Doctor banishes it back to the astral plane and Padmasambhava is able to die in peace.Only the second episode remains, though some fan reconstructions can be found online.
The Doctor: Yes, Jamie, I believe I have.
Jamie: What are you going to do?
The Doctor: Bung a rock at it.