Steven Moffat is Show runner and chief guiding light along with Mark Gatiss Sherlock Series 4 Premieres 1 January 2017 on BBC One.
What do you mean when you say ghosts of the past are coming back?
By ghosts of the past we mean consequences. There are consequences to the kind of mad cap in-the-moment fun lives that Sherlock and John and Mary lead. There are things that have happened, there are enemies that they have made, there is damage that has been done and some of that is coming back to visit them. There will be surprises and when some of those surprises happen you’ll think “ah I should have seen that coming”.
How have the main characters developed in this series?
That’s the whole story of this series, so I’m not talking about that! Events get out of their control for a while and we see them in their darkest hours and in their highest moments.
How does Sherlock feel about John and Mary’s new addition?
The thing about Sherlock Holmes is that he is a grown-up. We always like to pretend he’s an absolute lunatic but he does things well and he straightforwardly adores John and Mary, they’re his best friends. So he behaves probably better than most young men behave when their best mates are having babies. He’s pretty good at all that.
How strong is John and Sherlock’s relationship?
It’s a very powerful friendship. Now they don’t so much need each other as hugely enjoy spending time with each other. They are best buddies and they’re having the best time solving crimes together, they love it. At the beginning of series one they were two wounded beasts supporting each other, now at the beginning of series four they are at their best and the best of friends.
How has Mary affected their relationship?
Mary hasn’t affected the relationship with John and Sherlock at all. Mary and Sherlock like each other, I think Sherlock might have initially worried that he was losing his best pal but now he’s got two of them. She is a very smart lady so she knows that you don’t come between two best friends and allows and encourages that friendship to keep going. She herself adores Sherlock and those two actually have a quite separate friendship from Sherlock and Watson, so she hasn’t affected it at all, she’s enhanced it if she’s done anything.