Whether it's Corrie, a primetime TV drama or a stint at The National Theatre, Katherine Kelly's career defies definition. But her next step always relies on the writing, she tells Gemma Dunn.

Katherine Kelly has never been one to play it safe.

In fact, since leaving behind the cobbles of Coronation Street in 2012 (who could forget her stirring portrayal of brash barmaid Becky?), she's done little to appease industry snobs who dare to question a soap star's prowess.

Take her stint as the aristocratic Lady Mae Loxley in Mr Selfridge, for example, or her ruthless portrayal as editor-in-chief Maloney for The Field Of Blood.

Then came harrowing missing child drama Guilty; The Night Manager; Doctor Who spin-off series, Class; the action-filled Strike Back; and, of course, her depiction of stony-faced DI Jodie Shackleton in Happy Valley.

More recently the Barnsley-born actress even tried her hand at presenting as the host of gripping true crime series Murdertown.

"Well, I defy definition!" Kelly accedes, laughing. "But to be honest, the script is king for me, so if it's a good script, that really is the most important thing.

"Then very swiftly after that is the team," adds the 39-year-old RADA graduate.

"It's lovely and very flattering to be offered parts, but I still like to meet the team, because we're colours in the director's palette and I want to make sure that we're all going to be painting the same picture. Or at least a picture that we all agree on.

"There's so many different ways you can portray something," she notes. "So it does look like I make big, bold choices, but really I try not to take the path of least resistance. It's a contrariness in me."

She applies the same rule to her changeable appearance. And today Kelly - who has no qualms about altering her looks for a part - has switched her usual blonde locks for a sharp brunette bob.

"You can always tell by the hair!" she quips, teasing her next move. "There's a few things - something for ITV, which I definitely can't talk about...

"But this [style] is for a Netflix show that I shot in Madrid at the beginning of the year, [but] I don't think it's been announced that I'm in it yet, so I better hang on..." she persists. "But it's very different, surprise surprise!"

What Kelly can talk about, however, is her latest lead in ITV's latest gripping psychological thriller, Cheat.

Produced by the award-winning Two Brothers Pictures and penned by newcomer Gaby Hull, the four-part series centres on the dangerous relationship between university professor Dr Leah Dale (Kelly), and her student Rose Vaughan (played by the BAFTA-winning Molly Windsor).

But what begins as a seemingly open and shut case of academic deception soon spirals out of control, triggering a devastating sequence of events that threatens to engulf both women.

"On the face of it, Cheat is about a student essay that has been ghost-written by someone else. Perhaps!" Kelly says of the drama, which also stars Tom Goodman-Hill, Lorraine Ashbourne and Peter Firth.

"So to begin with it's about plagiarism. But the story quickly moves on from there and explores the theme of being a 'cheat' rather than that particular incident."

It's a page-turner, she elaborates. "It eats plot and I mean that in a really complimentary way. It's such a rollercoaster and it'd been a long time since I'd read a script like that.

"You know it's a thriller and you know we're in that genre, but you don't feel the twists and turns coming!"

Tipped to explore just how far we're prepared to stand up for what we believe - "It's that thing of taking things too far, isn't it? That's the joy of the drama" - the surefire hit promises to have audiences guessing from the start.

And that ruse is something both co-leads worked hard to maintain, insists Kelly.

"You can't put either of them in a box," she says of their title characters.

"We all have theories about what we're going to do, moral decisions, what we think is right and wrong," she realises. "And then [something] happens to you. Or to a loved one. And things can change."

Of the well-trodden hero-villain dynamic, she explains: "Molly, I and our director Louise Hooper wanted to make sure that Rose wasn't the baddie.

"That's what's clever about this script. It's not as cut and dried as that. Leah does some questionable things, as viewers will discover as the story unfolds."

Is the mother of two [Kelly shares daughters Orla and Rose with husband Ryan Clark] partial to a whodunit when she's the spectator?

"For me it's never about the genre, it's about the depth, and I will always give something a chance," she responds.

"I like to make up my own mind; I'm not one for reviews and other people's opinions. I listen to them and enjoy listening to them," she vows. "But I know that I can have quite an eclectic and different taste."

She follows: "The thing that makes me decide to continue to watch something is if I can't guess the way it's going to go - and that's to do with not just the overall plot, but the style of it and certain performances.

"For me, as an outsider, removing myself from this, I feel like I would be left guessing enough that I couldn't not tune in. It's all about the intrigue."

And amidst the "golden age of TV", there's certainly no shortage of great shows to watch.

We're in something of an exciting small-screen renaissance, Kelly muses.

"What's wonderful is that you always care about what you make, whatever genre, theatre, radio..." she states, having previously enjoyed a turn treading the boards as Miss Hardcastle in She Stoops To Conquer at the National Theatre.

"But what I've always loved about television is that it's in everybody's front rooms and they can just vote with the press of a button," she concludes.

"It doesn't cost an arm and a leg - ITV costs nothing, actually - and I like that it's up to the audience to decide whether they want to watch something or not!"

Cheat premieres on STV on Monday at 9pm.