There is something extraordinarily precise about Jodie Comer’s performance in Killing Eve, Phoebe Waller-Bridge’s brutal and unexpected entry into the spree-kill genre that took our top spot as the best TV show of 2018. Comer’s petrifying psychopath, Villanelle, is chillingly playful – like a mastiff that will take your throat out just as soon as it has finished with its ball – with the face of a schoolgirl. In real life, Comer is a wholesome 25-year-old scouser who, when she is not working, still lives at home. Yet she does something to the role to give it an oddly comic texture. Some combination of Comer’s humour – even the muscles in her face have comic timing – and her turn-on-a-sixpence quickness, mental and physical, makes her performance absolutely mesmeric. You are desperate to know what will happen next, even when you know full well that it will just be someone else ending up dead.

“What I loved about the kills, though,” Comer says, “was that it was always something you’d never, ever think. It was never ‘someone gets stabbed’. There was always something creative about it. She thrives off what she does, she cares about what she does, so it made sense to me that she would care about the detail.” They are, indeed, the murders of a psycho who cares: an embellished hair pin in the eye, a hair clip used to slice a throat, a baroque tableau of bodies arranged in the shortest possible time frame. (“Murder and great outfits. That show is everything I love,” said the crime writer’s crime writer, Denise Mina.)

Comer spoke to me from the set of Killing Eve’s second season, where she was filming with her co-star Sandra Oh. Testament to the success of the show, never minding all the award interest (two Golden Globe and two Emmy nominations), is that newspapers will run entire stories on what the two actors are wearing, a kind of elaborate costume-spoiler. (“The BBC darling’s teamed her fitted garment with a pair of matching high-waisted flares, which highlighted her trim frame with aplomb as she filmed the show’s latest plot line,” gushed the Daily Mail.) Where the critics had more than outfits to work with, they were near unanimous in their judgment. It was just stone-cold brilliant: “Slickly made and mightily entertaining,” we said. But, more than that, it was surprising and human: “Blade-sharp,” said the Times. It entered that exclusive club of cat-and-mouse dramas where people stopped comparing it to crime shows that had gone before. Perhaps because of its groundbreaking gender politics – a female killer and a female superbrain, it spoilt us with its defiance of convention – nobody seemed to mind the incredible amount of gore. Comer is surprisingly protective about this aspect of it: “What I loved about the violence in the show was that a lot of it was suggested to you; you didn’t see it. Some of it was gruesome. There was a lot of humour in it, or artistry. I don’t know if this is the Villanelle in me, defending what she does.”

Jodie Comer in Killing Eve. Photograph: Alamy

But the praise – Killing Eve has appeared on nearly every major end-of-year list – hasn’t made the show’s second season less daunting. “When you’re a part of a show that has been received so well, the thought of going back and doing it all again is daunting until you start doing it,” she says. “Then you just forget all that stuff and focus.”

If that sounds like the approach of an old hand, it is because Comer is: she had her first professional job when she was 12, when she got a part in a radio play. She didn’t have a hothoused, drama school upbringing – she went to a Catholic grammar school, did drama at weekends, and just happened to be one of those vanishingly rare 12-year-olds who is magnificent at it. “I’d say I’d been on screen since I was about 14. Well, I started working then. But I only became a real-life actor when I was about 17: that’s when things started to pick up. If I saw any of my performances from then, I’d want to punch myself in the face.” There’s a clip of a very young Comer on Holby City doing the rounds on YouTube. It is swaddled in comments about how cute she looks, when in truth, eight years ago, she looked very similar. She inhabits each part very completely; there is no idiosyncratic overlay that would tie Chloe in My Mad Fat Diary to Villanelle. Even in a small part in the slightly rackety school drama Waterloo Road in the earliest days of her career, her acting never seemed at all naive or uncertain. Again, underlining that she is extremely nice and not at all like a serial killer, she has a self-possession that makes her a very natural fit for the screen’s most nonchalant psychopath.

Her output has been more or less constant since, although she maintains that it just looks that way from the outside. “People get the impression that you’re working all year round because things come out one after another on the television,” she says. “They don’t realise that was filmed a year-and-a-half ago and you’ve been unemployed ever since.” She has had her share of lukewarm critical responses: she played Princess Elizabeth in the White Princess in 2017, which wasn’t for everyone. Her breakthrough role was as Kate Parks in Doctor Foster; a part that seemed to morph to meet her intelligence. She appeared as a generic young beauty and grew into something dark and intoxicating, manipulative and commanding. The extraordinary energy of that show, as if to foretell the dynamic of Killing Eve, is all between Suranne Jones – the eponymous doctor – and Comer. Not in the sense that they share a lot of screen time – rather, that they’re each so captivating that it’s a real wrench to move your attention from one to the other.

Jodie Comer with Sandra Oh in Killing Eve. Photograph: Alamy

Killing Eve, though, is in a different category of popularity, maybe partly because it was released in the US first and had a wave of approval and ready-made hype, but principally because it is just terrific. “With every drama, you don’t know how it’s going to go. Of course, I was obsessed with Fleabag [Waller-Bridge’s own breakthrough], so I always knew that whatever Phoebe touched turned to gold. But the style was so alien to me,” she says. “I second guessed every choice that I’d made.”

Was Villanelle little more than a caricature? Was she just really over the top? Comer went against her instincts to create the assassin. “I had this impression that, to do good acting, everything is minimal, really whispered, less is more,” she says. “What I learned playing Villanelle is that there is acting that can be so full of life and bold that it is ridiculous at times. There was something very freeing about playing her.”

Sandra Oh is an interesting counterpoint; she plays Eve, the detective tilting her world towards this one killer. The pair and the show have been greeted as a feminist triumph for so many reasons – the most obvious being the incredible relief of a bit of victim diversity, so it’s not always a young, naked woman who is dead. In Killing Eve, the unwitting victim is often a man in a suit.

‘Murder and great outfits. That show is everything I love.’ Photograph: Jason Bell/Sid Gentle Films

“If you look at other shows, it is always male-female; male killer, female detective,” says Comer. “It’s strange how, if you put two women in those roles, the narrative shifts. It’s something that we’ve never seen before and there’s something fascinating about it. Because women are so in tune with their emotions.” As the series unfolds, it is the relationship between Eve and Villanelle – with its intellectual intensity – that makes it so distinctive. “The two women are equally fascinated by and, in a way, scared of each other. There’s their age difference, they approach each other with real caution at times. I think it’s probably more of a question for Eve, really. Everyone feels that she has more control of the situation than she has.”

Spoilers are the smallpox of the streaming age, where viewers catch up at their own pace. So, even though I ask for them, I don’t truly expect any. All Comer will say about the forthcoming season is that “it has a different energy” and that we will get to know more about what motivates Villanelle. “People’s questions about Villanelle are always: does she have emotions; does she have morals? You know, we have these glimpses of her maybe feeling something, but what is it? What is it that we don’t know? That’s definitely something that we’ve explored in series two, whether she is battling with her conscience – what’s under there?”

In one way, the inner workings of the Villanelle conundrum are what I least want to see resolved. I could happily watch Comer and Oh in a two-hander, chasing each other across picturesque European kill zones indefinitely. Comer has created a mystery so bewitching that the worst crime would be to solve it.