Though he seems the coolest cucumber in the patch, actor Tom Riley is numbingly nervous. His legs quiver under the table, his mouth is dry, sweat is creeping down the back of his neck.

To watch him at a press conference, you'd never guess any of this.

Later, seated at a small table in a boisterous lounge of a hotel, he says, "I look so relaxed and so chilled, but the truth is I need to just not let my nerves get in the way of it. People do assume that I'm absolutely fine."

That same has proved true of his performances, the latest of which would tax a Buddhist monk. The British Riley is starring as the flamboyant and volatile Leonardo da Vinci in "Da Vinci's Demons," premiering April 12 on Starz.

Riley admits he shares one quality with da Vinci – a driving perfectionism.

"And that was my way into Leonardo – with him nothing would ever be right, nothing would ever be perfect, nothing would ever be finished."

Riley, who has starred in British TV's "Monroe" and "Lost in Austen," says he didn't have time to become nervous before he auditioned for the role of the artistic genius.

"(Writer-producer) Daniel S. Goyer and the other execs were over for the weekend for four or five days and I just lucked out, went in, and it went really well. The next thing I knew I was flying out here to meet Starz."

When he first read the script, he was stunned.

"Usually as an actor you read a part that's amazing and you think, 'I want this so much that I'm obviously going to ruin the audition. I'm going to be too desperate. I love this!' But I didn't have time. I got it quite late and didn't have time to get nervous, so I just came in and did it off-the-bat, and it worked out."

It's been a lifetime struggle for Riley caging his own demons.

"When I started acting I was micromanaging every choice I made. 'Do this. Keep your hands on the steering wheel.' 'Make sure you do that.' 'No, no, that will be perceived wrong.'

"Then about two or three years ago, after a play, something else happened and I went, 'You know what? Stop trying to decide, because you never know.' As an actor you take a job, the script might be brilliant, but 100 things can go wrong before it comes to the screen. I just thought, 'Take your hands off the steering wheel and let's just see where the car rolls …'

"Since then that ability to not give yourself such a hard time has afforded more chances.

"I do occasionally stop myself from doing things I should because I'm too nervous. You should give yourself allowance. What can you lose? … What's the worst that can happen? We're so lucky to get to work in a world like this."

Actually, Riley – who'll be 32 on Friday – has been working in a world like this since he was 5, performing in local theater. He majored in literature in college, having no clue what he'd do with a degree in literature. But, again, he was a victim of his passion.

"When I was young there was a mobile library that came to town, a caravan of books. We didn't have a library where I lived. And my mum used to drop me off with the librarian at the age of 8 and I would just sit in the corner of the mobile library and read from 9 to 6 p.m. when Mom got off work. I just loved books and loved analyzing things. I loved literary analysis and film analysis but was too scared to go straight into acting, which is why I majored in literature."

After graduation he attended drama school and was still there when he landed a film role opposite Juliette Binoche.

"Because I knew I was working opposite her and was the male lead in the role, I just didn't want to get it wrong," he says.

"Every night the cast would go … out for dinner and I'd say, 'I have to go home and work on tomorrow.' As the shoot progressed I ran out of time to do that. … I get better the less work I do because I've stopped thinking so hard, stopping figuring that every word must mean something – old drama school training, you know – act on every word. And suddenly it's freer."

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