It's 25 years since the Good Friday agreement halted hostilities in Northern Ireland, but as wrangles over the Brexit deal show, The Troubles haven't entirely disappeared.
Tim Edge's darkly comic thriller Under The Black Rock tracks back to 80s Belfast when young people were drawn into violent extremism.
Niamh Ryan is played by Harry Potter actor Evanna Lynch, who says the play is set in a world where "you don't know who to trust and you have to question everyone's motives."
Growing up south of the border, Lynch was only seven when the agreement was signed, but had an "awareness of this secrecy surrounding Northern Ireland."
"We didn't go to the North because my family were Catholic and the impression was if you went there, you don't know what would happen," she says. "I had this understanding; don't ask questions, it's a touchy issue, better not to talk about it."
Rehearsals at Hackney's Arcola Theatre have involved "challenging everyone's prejudices".
"Theatre is a place where it's safe to have uncomfortable conversations and explore prejudices without judgement," says Lynch, adding that the play examines motives for extremism.
"Everyone's were different; family, religion, the excitement of being involved in a conflict. But just as you think you understand these characters and their motives, you realise you don't know anything."
Niamh is trying to prove something to the paramilitary father who belittles her.
"It's mostly young people who get pulled into these radical groups, they ask big existential questions like what am I doing with my life, how will I make my mark on the world? Niamh becomes a dangerous person yet there is so much vulnerability; childhood wounds, and an innocent desire to impress her father. She's morally conflicted; she does extreme things, but has constant doubts."
But how does humour fit with such serious themes?
"The darker the story the more room there is for humour. There's this comic absurdity in Irish plays, it's a survival mechaism for the Irish and Northern Irish people. If we had to really acknowledge the tragedy of The Troubles, all the innocent lives lost, we would fall apart." 
As a bookish child battling anorexia, Lynch escaped into literature, including JK Rowling's books. She wrote to the author, who replied with letters stamped 'by owl post.'
"I was 11 when I started writing to her. It was incredible luck that she even saw that letter and wrote back," says Lynch.
"She has an enormous heart and reaches out to vulnerable people. I clearly loved the books, and was going through some mental health difficulties."
Then came an open casting to play Luna Lovegood in the last four films. Lynch beat 15,000 others to the part, with critics praising how she inhabited the role, and Rowling saying she had Lynch's voice in her head when writing the final books.
"That's the biggest compliment I ever had. When I read the books I read in my own voice, it didn't occur to me to change my accent and no-one asked me to."
She adds: "It was a huge deal to go to London, my parents are teachers who didn't have much disposable income, but my Dad is a sports fan who loves a challenge and having the odds against you. It was a fun journey, him and me on this crazy mission. Knowing those books inside out gave me the confidence to go for that audition. I had this private conviction that I wouldn't go wrong if I stayed true to my interpretation of this character who had touched me deeply. I went to that place in my head when I read and it was just me and the character."
Being on set was "fun and exciting" although she hated doing school work.
"Some of the young actors had stopped education and I was hugely jealous learning my Irish verbs when they were out playing guitar! I had a sense of being left out of the social bonding that happens when everyone is sitting around, and felt 'I can do my exams any old time but this Harry Potter filming is only once.'"
Learning on the job she was "exposed to incredible acting" but also "sheltered and cosseted."
"I couldn't have done it wrong, there were 20 people focusing on making sure you were good. I would do my bit of acting and trust the director knowing it would turn out fine. Later doing small budget projects, I realised, you have to take responsiblity for yourself."
Lynch who has written of her mental health struggles in 2021 book The Opposite of Butterfly Hunting, doesn't enjoy the attention that comes with the Potter juggernaut but admits it has offered opportunities.
"In the early days there wasn't social media and we were kept separate from awareness of the scale of it. I find it strange. I have an interesting inner world but I don't think I am that interesting a personality to have this many people interested in me!"
She adds that the thought of being "a kid who got lucky gets in my head sometimes".
"Every time I start a new job with actors who have done the normal route, I feel I have to prove myself. I often think where 'would I be if I hadn't got it?' I don't know if this career would have been available to me. I am not a natural actor I live in my own head and don't like attention on me - celebrity red carpet interviews aren't my comfort zone - but I am grateful it pushed me into this visibility where I get opportunities I wouldn't otherwise."
Her drive to act is a desire "to be at the heart of stories".
"I need to remind myself; I am a book nerd who got into this because I love words and language."
And Lynch's next job has a bookish edge, playing James Joyce's schizophrenic dancer daughter in the movie James and Lucia. Lynch is intimidated by Joyce's reputation - her uncle is a Joycian scholar, and she hasn't read Ulysses - but is fascinated by Lucia, who "trod this line betweeen her art and mental health."
"It's no mistake my career started playing the oddball in Harry Potter. I relate to the outsider, to people who don't fit in."
Under The Black Rock runs at Arcola Theatre Hackney from March 2-25.
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