Back as the supreme sleuth on BBC One on New Year's Day at 9.00pm, Sherlock star Benedict Cumberbatch talks about what's in store for fans in series three.

How did it feel reading the first script of the new series?
Benedict Cumberbatch:
It's always a kind of cold-faced thrill because you get the first enjoyment of it. It's like being the first audience of the finished product, so it was a real treat. We knew what the rough trajectory was over the three films, but when you get the full script it's just a delight. The first thing I go to is the big scenes, and every one of those scripts is a terrific read. It's such a joy to read them for the first time – you get that thrill that hopefully the audience will get when they sit down and watch it.

What was it like getting back into character after a two-year break?
I would say it was easier than the second series, but it's never completely easy because of the break and because of how extraordinary a character he is. No matter what comparisons people draw between me and him – he is very different in his temperament, he is more mercurial, his rhythms are faster and more aggressive than mine are, and that goes for his intelligence and speed of talking – I feel like I have to ramp up a gear which takes a bit of time to get used to. But you know, I love it and however hard it gets, and it is a tricky one to pull off, it's a character I love playing and I always feel sad saying goodbye to him.

What do viewers have in store for Series Three?
Without giving too much away there is a fantastic trajectory in Sherlock's character arc which is going from a position of not really fitting in and then doing incredibly well and forming a bond again with John (Martin Freeman).

They have some extraordinary adventures in the first and second episodes and then in the third they are challenged by a situation and a master villain who brings him to his knees. What's exciting about this series is we see Sherlock in real peril. We know from the end of series two he staged his death, he was out of the game but calculating every move and therefore in charge. With this challenge he really is out of control. He really does lose his authority on the situation and it's really exciting to see a hero in that much jeopardy and it's very interesting to see what it does psychologically to him.

As far as plot goes, Sherlock and John reunite, there is an explanation and there is a new character in the shape of Mary Morstan (played by Amanda Abbington) – it's really about how the three of them kind of coexist. It doesn't become a trio, but she is a leading figure in it, she's not just a stay-at-home wife. She is someone who is very involved in both of the boys' realities, but it's a wonderful new dynamic to play with.

Do you think Sherlock will understand John's reaction to the news that he is in fact alive?
I think he completely thinks that John will understand what he has done, and be fine with it. I think he is expecting a wry smile, a handshake and maybe a laugh or two and then off on a case. He gets it so wrong, so, so wrong. He's rusty, he regresses and it takes him a little while to get on form, to smell out London and understand that again and also to get back to being best friends – you empathise with him because you know ultimately he did what he did to save his best friend's life. But John being quite a straight-laced ex-soldier is not too happy.

Do you think there is an evolution in their relationship?
They start from a point where they are almost strangers again, they have to have that moment of trust re-established. It's quite a thing to do to a friend to fake your own death to save a friend, and it takes time.

They rile each other and amuse each other and excite one another and do everything that good friends do but to extremes because of the situation. And the friendship just grows through very heightened circumstances and drama.

It's just a glorious thing to play out and having such a skilled actor as Martin Freeman to play off – the verisimilitude is bar none and his reaction and comic skill is [sic] always exceptional. But the real heart of what he does and why he is so funny is because it's from a place of truth.

In Sherlock you've got this ridiculously theatrical, sometimes manipulative but very real friend which makes for a tempestuous but brilliant odd couple friendship with all the dynamics of series one and two, just playing out in very different circumstances.

If you could have one of Sherlock's attributes what would it be?
His mental focus, which comes with its faults as well – it's very hard-earned. What I love about him is he is a hero for people who are different and a role model for people who are different because he acquires a status through his skill that is bar none and I would love to have his mental agility and focus. I just think it is exceptional... and his memory, if I can have two!