"I haven't done much work," said Florence Pugh, crossing her legs on a restaurant sofa in Park City, Utah, following her debut at the Sundance Film Festival in January. "I'm very much a newbie."

It's unlikely she will be new to the public very long. The 21-year-old English actress is likely to be considered a bona fide breakout star after playing the lead in "Lady Macbeth," a spellbinding romantic thriller set in early Victorian England. In William Oldroyd's handsome film, her character, Katherine, is enigmatic, seductive and very dangerous. Despite the title, she's not based on Shakespeare's femme fatale but a model of her own design, seemingly a proto-feminist heroine one moment and a fiend the next.

Landing such a colorful and complex role at the beginning of a career she was determined to have since age 7 is, she admits, a "fluke." Coming from a family well-stocked with performers, she has acted, vocalized and performed musically for 14 years, a regular at school shows and talent competitions.

"I've always wanted to act," she said, with no Plan B in reserve. "I'm no good at anything else. I'm good at singing, acting and playing guitar, and that's it. If I don't make a profession out of that, I'm probably going to fail at life very, very hugely."

Having won wide attention and significant accolades for her film work in Britain, she said she feels as if she has been "just kind of catapulted because it was with a great director and really good production. It does that, those films."

Playing the intricate Katherine three years ago at 18 included many challenges, from keeping the audience invested in a shocking character, to extensive nude scenes, to her first experience of shouldering and firing a large rifle.

"I was ready for it totally. I didn't feel like I needed to go leaps and bounds to be this character," she said. "I'm a strong believer that the person who is playing that part is at least 40 percent of the role. That's not to say that I'm a psychopath," but that her character's actions, no matter how violent, were based to a degree on self-defense. "She's put in this situation and she's trying to make it hers. She's doing the best to try to control whatever it is that she thinks she has. And she's just trying to enjoy it."

Pugh set out to make viewers appreciate the character as well, however calculating and cruel she may be. "It was quite obvious to me that I needed to make her lovable. You need to love her, you need to recognize her" as she channels her fight-or-flight reactions to a wretched marriage with a dreadful heir who holds her virtually imprisoned, an unmasked affair with a lustful servant and scandal spreading like wildfire.

"I've never believed she was a bad person," Pugh said. "I know that she does bad things. I don't think she's a bad person. I think she is pushed and tested and like any normal person when you're told to sit in a house all day long, she's going to want to fight back.

"My perception on her? I think she's delicious. I found it quite important to make her incredibly likable. You can't follow a killer through the entire film and feel something for them if they're genuinely malicious."

The hardest part was "fitting the corset in my dress. You get in and you realize you can't breathe, you can't walk. That opened my eyes to how these women lived. They were put in these outfits the moment they got up until they went to bed. You're silent when you're in it. You can't really breathe and speak much."

She felt her unclothed love scenes were challenging to film, but found them beautiful to view afterward. What bothered her more was a scene where, in a single unbroken take, without benefit of computer effects, she turns a rifle on a horse, fires and sees it collapse.

She called the horse, a film veteran, "one of the most phenomenal actors I've ever met. It's utterly incredible.

"He's a working horse, and after three goes he gets a bit grouchy and he's done with work. They have to put padding down underneath, so it's a really healthy fall. So we shot the first go, and, genuinely, I thought I shot the horse. I screamed out loud, and I screwed up the first take. It was terrifying because it wasn't about instinctive acting, it wasn't about what you find in the moment, it is about 'On the count of three you're going to pull your gun back and this horse is going to bounce up in the air.' "

What she didn't know was that firing a blank cartridge would also push her backward.

"I had never done a gun before and they said, 'Obviously, it's going to be quite a shock and you're probably going to fall back a bit.' I said 'OK, cool, you want me to fall?' And they said, 'Yeah, fall on the floor.' I didn't ever do that movement in my life. So I did it and literally fell back like I just launched a rocket. It was a hard, hard day."

It hasn't made her consider another line of work, however. "I could do lots of films now, not in like a cocky way but if I really wanted to work," she said.

Pugh has just wrapped starring as English professional wrestler Saraya-Jade Bevis, better known as WWE female superstar Paige, in "Fighting With My Family." The comedy, based on her real-life story, is written and directed by "The Office" co-creator Stephen Merchant and produced by Dwayne Johnson, who makes a cameo appearance, presumably reprising his former role as The Rock. Pugh also will star opposite Liam Neeson in "The Commuter," an action thriller scheduled for release next year.

"I really want a role that excited me as much as this one," she said. Ideally, "I would really love to do a western, like really, really. I would really love to be like a badass girl on a horse with [pigtails] and cowboy boots. I would love that. So if there's anyone out there" she'd quickly join such a project. After all, in addition to the acting, singing and guitar picking on her résumé, she knows how to perform opposite a horse.

@colincovert