Andrew Scott reveals the method behind the madness of Sherlock‘s nemesis, Jim Moriarty…

We’ve only seen Holmes’ evil nemesis, Jim Moriarty, a few times so far in Sherlock. In this weekend’s final episode (BBC1, Sunday) he’s back with a vengeance. What can we expect?

“The thing with Jim Moriarty is you don’t know what you’re going to get when you see him! You know he’s going to appear, but you don’t know what mood he’s going to be in – or what he’s going to do. There’s a real sense of unpredictability with him.”

He’s an iconic character; were you worried how your version of him would be received last series?

“I was nervous I was going to mess it up! I tried not to over-prepare him or plan too much, as I think an audience can sense when something’s been thought out too much. It was important to me that he was playful. I knew he needed to be both funny and scary.”

In this episode he’s planning an atrocious crime that involves the Tower of London, the Bank of England and Pentonville Prison. What drives him to do the things he does?

“Like all terrifying people, there has to be a reason why Moriarty acts as he does. We just don’t know what it is, and nor does Holmes! For me it’s important that I don’t feel like I’m playing a villain. You have to look into yourself and ask ‘what would I do?’ There are lots of shades to Moriarty and he’s very surprising. We can ask the question, but we never really know why he does what he does.”

It seems like Sherlock and Moriarty really like interacting with each other. Why is this?

“There’s a great sense that the two of them enjoy it enormously. It’s a great game to them both. We see different sides to Sherlock and Moriarty when they’re together. They enjoy trying to outdo each other. Playing Moriarty is a gift of a role for me. Moriarty’s flirtatious with everybody, but he has a manipulative charm about him.”