For Irish actress Evanna Lynch, 26, the Harry Potter films were a catapult to global fame, the type that lasts a lifetime.

Lynch became famous overnight playing the kooky young witch Luna Lovegood in the wildly successful film franchise, achieving the kind of recognition that meant she was recognized everywhere before we knew what kind of actress she would eventually become.

A clearer picture is starting to emerge now. This month Lynch is in New York starring in the 20th anniversary production of Enda Walsh's Disco Pigs, in what for this reviewer is the definitive production of the award winning 1997 play (the original cast included then unknown Irish actors Cillian Murphy and Eileen Walsh). 

It's a wise new career move for the gifted Irish actress who once competed against 15,000 other girls to land her coveted role in the Potter films in 2007,  eventually leading on to other screen roles and of course to her 1.2 million Twitter followers.

Starring alongside young Dublin actor Colin Campbell, the sparks that fly between the two Irish leads onstage are instantaneous. A star-crossed pair of friends and would be lovers, Lynch's role represents a dramatic departure from her Potter days, to the benefit of both the play and her rapidly expanding acting range.

On the surface Disco Pigs is about two working class kids from a dead end street in Cork who find that their only truly enduring support is in each other. So together they retreat into an imaginary world, mostly to escape the world that they were born into. It starts off as a sanctuary but it starts to become suffocating.

This alternate world they have created has it own rules, its own laws and its own language, and they even give each other their own names, Pig and Runt. Inseparable since childhood they are an increasingly codependent duo who are suddenly taking the occasional misstep now that at 17 their budding sexualities are entering into the mix.

For an actress intent on demonstrating her range the play really is a perfect vehicle. But what you might not expect is just how good the new production at the Rep actually is. Starting its life at the Trafalgar Studios in London, this 20 anniversary production of Walsh's breakthrough play is a high-octane piece of physical theatre that is so seamlessly designed it let's Lynch and Campbell inhabit their knockabout characters and tell their story in a way that almost looks effortless.

Lynch is so convincing as the girl slowly stepping out of everyone's shadows (including Pig's) that you fear for her resolve and for her safety. Finding her feet in a hardscrabble world that thinks nothing of knocking her right off them is heroic in itself, and though she may be nicknamed Runt she's far from a pushover.

What lifts Lynch and Campbell's production head and shoulders above every other production of Disco Pigs that I've ever seen is the pure physical theatre that the pair have perfected. Their relationship, their codependency, the opportunity and threat that they represent to each other is captured in every single move they make on stage, allowing their body language to say even more than even the script does in this brilliant production.

Disappearing into someone else so that you don't have to confront yourself is a story as old as time. As Disco Pigs progresses we being to see that Runt wants to escape herself. She wants a new life with new people and a new beginning. She wants to try on new personas just like a new dress.

Pig on the other hand rejects everything that isn't Runt and doesn't want anything in life except her devotion. He feels the shame of his town's cold rejection and his anger drives him. The only good thing in his life, the only thing that makes him himself, is the way he sees himself reflected in Runt's eyes.

How you feel about the amplified Cork accents and the invented language of this passionate pair may fluctuate as the play progresses. This after all is a debut play where the pop culture of 1996 (there are multiple Baywatch references) really hasn't traveled from the era of grunge, but at its core of Disco Pigs is still a timeless struggle that will pull anyone in.

We don't want this troubled pair to stay together but we also don't want them to break up. The thing that that's brilliant about them is their unbreakable bond, but it's also what makes them so dangerous to each other. That push and pull tension eventually sees their lives speeding out of control.

Pig has what psychologists call love blindness for Runt and for the most part it's reciprocated. “Jarr my bes pal in da whole whirl,” says Pig. “Jarr my life, Pig,” Runt replies. They worship the ground each other walks on, but you slowly start to wonder why.

Pig hates anything that isn't exactly like himself and that list includes nordies, lads who wear tank tops, Sinn Fein voters, people who try to dance with his best girl, anyone who looks funny to him or looks at him funny. Violence is his preferred solution to any kind of social complication. He's a time bomb looking for a place to explode.

Just as Pig's navigating toward disaster Runt is navigating toward the shore. Pig is the last to notice they've been rowing in different directions. The most moving part of the play is when Pig serenades Runt with the song Be My Baby unaware that she's being violently assaulted as he's pouring out his heart.

So from its opening moments we start to infer that Disco Pigs is a speeding train that's coming off the rails, but Lynch and Campbell never allow us to get too far ahead of their bruised and broken characters.

What makes this production so worth catching is all the layers of desperation they reveal. Beneath all the pub fueled bravado these are just two lost kids with no one looking out for them and no place to go.

Campbell makes you feel his characters shame, the shame of being looked down by others over his cheap tracksuit and his working class background. He knows that he's been judged and dismissed by the world before he opens his mouth.

Only Runt sees him and only Runt loves him and when that relationship is threatened his road runs out. Disco Pigs is a story about adolescent obsession and its attendant dangers, but it's also about Walsh's preeminent theme, what happens to lonely misfits when the bigger script has no more roles for them.

In Disco Pigs the roads run out long before the final curtain and Lynch and Campbell have delivered a masterclass in showing how easily cruelty can replace compassion, with life changing results.

Disco Pigs is now playing at the Irish Repertory Theatre.