With the final curtain having fallen on the original cast this month, Louis McCartney’s London West End chapter is coming to an end. For 11 months, the 21-year-old Northern Irish actor played young Henry Creel in the award-winning Netflix stage production of Stranger Things: The First Shadow, an official prequel to the sci-fi series which returns for its fifth and final season sometime in 2025.

“I’ve become extremely sentimental,” McCartney tells me when we sit down for coffee at Covent Garden Hotel Brasserie, five minutes away from the play’s current home, the Phoenix Theatre. “I have this fantastic relationship with Patrick Vaill, who plays Dr. Brenner, and we’ve kind of cultivated and grown this very fucked-up bond, which is based on love and power. And we were only able to do that through our trust in each other.”

He doesn’t have to say goodbye to the character quite yet. After breaking box-office records in London, the show – which boasts some of the most cutting-edge special effects ever seen on stage, courtesy of Harry Potter And The Cursed Child illusionists Jamie Harrison and Chris Fisher – is transferring to Broadway in March.

“I cannot wait to do it all again in New York,” says Louis who’s reprising his role.

The First Shadow, written by Kate Trefry from an original story by the Duffer Brothers, Jack Thorne and Trefry, takes the audience right back to the very beginning. Set in 1959, 24 years before Will Byers’ disappearance in Season 1, it offers answers to some of the more pressing questions Season 4 has left us with. First and foremost, the origin and source of power of main antagonist Henry Creel, aka Vecna.

His professional stage debut, Louis’ portrayal of a troubled kid’s slow descent into madness has earned him the Critics’ Circle Award for Most Promising Newcomer and the Stage Debut Award for Best Performer In A Play.

“A lot of Henry came pretty naturally to me,” he continues. “I’m a smaller guy, so in school I learned to be strong in myself and that I don’t depend on others. I used a lot of that feeling, not so much emotional recall, more by placing myself in Henry’s shoes reimagining my life as a little boy, who doesn’t know what’s going on in his mind, who just wants to fit in, fall in love, do good in school and do good with their Mum and Dad.”

Most fun and challenging to him was the movement of a character constantly swaying between boy and monster.

“I don’t even know how I do that,” he confides. “It’s taken like six months to get there. I’ve been in pain for about a year, my neck is always killing me, but it’s very worth it.”
He recalls rehearsing for the epileptic fit featured in the show.

“The director, Stephen Daldry, brought in two of his friends, one of them is an epileptic and the other one kind of follows him to make sure he’s okay. They actually mimicked it for me, he just started screaming and convulsing. I was like: ‘Holy shit, I have to do that eight shows a week!’”

Voice coach William Conacher helped him perfect the characteristic Vecna voices: “a big deep one” and “a more gravelly vocal fry version”, as Louis explains. In addition, they worked with the same modulator used by Jamie Campbell Bower, who played Henry in the series and greatly inspired Louis’ performance.

“When I put on the clothes, it was like putting on his laundry”, Louis says. “I did a lot of work studying him and watching his famous monologue with Eleven in the Hawkins Lab. And I really admire his performance. He plays a psychopathic killer with great charisma and charm. And he’s very enigmatic. I looked at what he had, then sort of tied a rope and walked that every night for three hours to piece the two stories together.”

Does he have a favourite scene, I ask him.

“I love the killing scenes. This whirlwind of death and betrayal and love. And it’s so enthralling to work with the projection of the smoke, that is Henry’s powers. The illusions have to work with me or else it looks like they’re overpowering me. I also loved working with Ella Karuna Williams, who played Patty. The locker scene, when they first meet, is very cute and a good set-up for the story, kind of weaving this false narrative that everything is going to be fine.

“Our goal is to make you feel for Vecna, which is almost impossible. Henry has this ability to make people think that he can do anything, but he’s also strictly contained by the people around him. Meanwhile, I think who he wants to be almost has the power to overcome the story.”

Despite his current success, McCartney had to be somewhat pushed into acting by his screenwriter dad.

“He taught me what a good work ethic is, because he is heavily ambitious, and I really look up to him,” explains Louis, who studied drama in school and later joined the Belfast School of Performing Arts. He also made YouTube monologues with his dad to try to find him an agent.

“We got like 100 subscribers. And we thought we were famous,” he laughs.

At the age of 18, he started the nine-month Screen Acting Programme at Dublin’s Bow Street Academy.

“I realised that my main takeaway was that they weren’t teaching me acting, they were teaching me how to live,” he recalls. “Day to day, they said the first step of acting is living. You go to an art gallery and experience life and think about that painting, and someday that would be called upon by you, by a character, and it will influence something in your work which will produce something in your eyes, the way you speak or the way your character walks.”

Living in Dublin also brought him closer to his Irish heritage, hanging out at the Workman’s Club with his best friend Alan Markey, going to Bonobo for pizza and a pint, or Fresh in Smithfield Square for lunch every day.

“In Belfast, the thing that we’ve mainly got is the Troubles and getting past that. But down south I experienced the other side of my culture, which was Irish pubs and trad music and the Dublin accent.”

Louis’ first job was on Season 8 of Game Of Thrones where he was killed by Khaleesi’s dragons.

“It was the big, moving steadicam shot through King’s Landing. I’m in it for like a second. But the experience was great.”

Later on, he was on the BBC Northern Ireland soap, Hope Street, for three seasons. Louis stresses the importance of staying true to yourself.

“I think it’s so easy that you let your ego get in the way of things. I met my girlfriend on the job. She really helps me remember who I am.”

Without some key people in his life, he would not be where he is now, he tells me.

“Outside of work, my life is just filled with love and people, and that makes the job so much easier.”

But he is also sure that he can reach anything through “a little bit of luck and a lot of hard work”, as his dad has taught him.

“There’s so many great Irish stories about working class actors who’ve come up through the ranks and made their golden path through their talent, dedication and ambition. Anthony Boyle would be somebody that I look up to, and someone that I almost aspire to be. What I really want is to be myself, make my own impact on the industry and prove what I can do creatively.”

Workshops for the Broadway play are starting soon. But what comes after?

“I think I’d like to do something like Beautiful Boy with Timothee Chalamet, something I can sink my teeth into and that really touches people,” Louis concludes. “I also really like the fantasy series Eragon, and I’d love it if they ever did that. In terms of theatre, I’d love to play the MC in Cabaret, because it’s a fantastically weird character and we all have a fascination with things that scare us.”

• Louis McCartney will make his Broadway debut as Henry Creel in Stranger Things: The First Shadow. Previews begin March 28, 2025 at the Marquis Theatre, New York.