3x08 Episode 8 [season finale]
Aww, everything's resolved Happily Ever After... until the Christmas special, anyway. And series four, of course.
[Watch it (again) on ITV Player.]
10x06 The Beginning [season finale]
Aww, everything's resolved... except it isn't, because there were those couple of mentions of Kochanski that didn't go anywhere. So, Series XI? After the ratings this got, I expect so.