Back as John Watson in Sherlock on BBC One on New Year's Day at 9.00pm, Martin Freeman talks about what's in store in the new series and its opening episode, The Empty Hearse.

Warning: spoiler alert!

Two years have passed since Sherlock (Benedict Cumberbatch) faked his death. How do you think this has affected John and how has he moved on?
Martin Freeman:
His best friend has died horribly in front of him, which took a long time to get over, but the way that his life has moved on is that he has fallen in love with Mary (Morstan, played by Amanda Abbington). He is leading a functional, normal-ish life, really, which doesn't have the highs and lows of his life with Sherlock but is certainly a bit more steady. But there is a sadness with John which will always be with him when you lose someone that you love - he is slightly dulled by life.

Could you empathise with John's reaction to Sherlock's reappearance?
I can completely empathise. If someone came into your life after you thought they were dead it would be a major event, and given that Sherlock is the way he is, he winds John up a lot, and that is when they are getting on! But coming back from the dead - John is hit very hard by that.

What is it about Sherlock that inspires such loyalty from John?
He's a pretty magnetic bloke. He's very intelligent and there is something mesmeric about his obsessiveness as well. He's the cleverest bloke that John has ever met and he likes that challenge and the share of the danger as well. Because John is ultimately into danger as well: he is a solider and a doctor so he is around situations that are perilous and a bit tasty. So he responds to that in Sherlock and he just wants to be around him - I sometimes don't even know why!

Are you surprised by the massive online reaction to the show?
I don't think any one of us could have dreamt that there would be that sort of reaction. Never mind online, but the entirety of the success that it has had we could never have dreamt about. People used to ask me about The Office. They would say, 'Did you know it would be this huge thing?' and there was certainly no way we could have known how big Sherlock could have been. I would have settled for it being a really good show that some people really loved. But the fact that it has been feted and honoured - we could never have spotted that coming.

And the online thing is certainly a thread of our fanbase - and it's a very vocal one. I think what's important not to forget is that it's not the only one; there are so many people who just watch it on BBC One when it comes out and love it. But the online thing is surprising in a way because they have almost created another world, especially if you are over 30 because it still seems like that stuff is really new. Especially the sort of reaction we have had, I mean, other shows do get it as well, but we are one of those shows that people go absolutely barmy for. And it's nice! I'd much rather that than people ignored it!

What do viewers have in store for this series?
Lars Mikkelsen (who plays Charles Augustus Magnussen) is fantastic; he is a brilliant villain. For those who will miss Moriarty, which is totally understandable, we have another fantastic nemesis for Sherlock and John - he does it superbly. Of course, having Mary Morstan around is good because that adds another dynamic to Sherlock and John's relationship and another dimension to John's life. It was great having Amanda Abbington on board - she was brilliant, I like working with her!

What's been your favourite episode to date?
I have to say the ones that we have just filmed have been brilliant. Before that, probably Reichenbach (Fall, series two finale) was my favourite one to do because when we read it I was really, really excited and I thought the finished product was amazing. It was one of the best things that I've ever done and am likely to do for a while.

But then I found that about the episodes we have just done. It's particularly important you end on a fantastic third one and the third episode in the third series is stellar. Everyone's work on it is great and it's a (co-creator and co-writer) Steven Moffat special, which is always good - but they are all so good! I was very, very excited when I read this one - it's one of the best scripts I've ever read.