20x22 The King's Demons Part Two [season finale; 3rd watch]
What an odd ending. Essentially, the Doctor uncovers the Master's plot... and then all the time travellers just leave. There must be some very confused 13th Century nobles left behind, but we never see any of that. The downsides of being only two parts, I guess. You have to wonder if three is the ideal length for a Who story -- two is a bit rushed and unsatisfactory, whereas with four (or more) a good deal of the middle episodes is often spent doing sod all.
1x16 (8/9/14 edition)
1x17 (9/9/14 edition)
[Watch episodes 16 and 17 (again) on iPlayer.]