What is Sister Julienne up to this Christmas?

She has a particularly busy Christmas. There is an exploration of a new medication for fertility which brings with it a mother who is expecting twins as a result, which is wonderful. The birth all happens rather excitingly and it was quite something to film - there were a lot of people crammed in a very small space. I always enjoy childbirth scenes, but this particular one was a very difficult one to film; interesting but just a bit cramped.

What else is going on with her?

Sister Julienne is always worried about Nonnatus House, although we're in a pretty good place financially, and she’s got ideas about the future. And the only other concern, as winter approaches, is Sister Monica Joan. Winter is tough – something you need to get through, and Sister Monica Joan feels she’s not going to get through it and won’t be there next year. She is very low, very depressed and it is up to Sister Julienne to help her see that there is no reason to believe these dark thoughts and that there is a great deal of vitality in her.

Trixie’s brother Geoffrey (Christopher Harper) returns after we met him at their wedding – what has that been like?

He's just such a lovely, fun character to have around – totally unpredictable. As an actor, Christopher is just great fun and we all just enjoyed his company. So, we're all very much hoping he'll appear again. It seems he may be homeless when he arrives to stay with us. I don't know what the future might hold for that character, but it would be it would be lovely to see him again.

How Christmassy is this year’s special?

This is very much Christmas at home at Nonnatus, but it doesn't at all miss that whole magical sense of Christmas. It is quite a special Christmas for everybody. There is something in there which is going to be a surprise to everybody. It was a lovely surprise reading it. It's totally unexpected. There's quite a build up to it and I can say no more.