This was a six-part serial, first broadcast between 30th September 1967 - 4th November 1967. The serial was written by Mervyn Haisman and Henry Lincoln, produced by Innes Lloyd and directed by Gerald Blake. The script editor was Peter Bryant.
What I've seen:
Episode two. The other five episodes are lost.
Accompanied by Jamie and Victoria, the Doctor visits a Tibetan monastery in order to return a sacred bell that had been given to him for safekeeping during an earlier visit. The Tardis crew don't receive the warm welcome that they expect. The abominable snowmen of the title - the yetis that have always lived peacefully in the mountains surrounding the monastery - have turned into killers, and evil lurks in the monastery's inner sanctum...
The good news:
The somewhat less good news:
Another singleton that's worth seeing.