When orchestrator, arranger, and musical supervisor Alex Lacamoire met composer and lyricist Justin Paul for dinner back in 2013, Lacamoire recalls, a “mutual admiration society” was created. At the time, Lacamoire’s various Broadway credits included two collaborations with Lin-Manuel Miranda, In the Heights and Bring It On: The Musical. (A third would follow, in the form of a little show called Hamilton.) Paul and his creative partner, Benj Pasek, had written scores for A Christmas Story: The Musical and Dogfight, which had made them rising stars in the musical-theater community. (The pair would soon branch out into films, among them La La Land and The Greatest Showman, and would eventually win their own Tonys, Grammys, and Oscars. Lacamoire also worked on Showman, among other screen projects, including FX’s recent Fosse/Verdon, and would win his own Grammys, Emmy, and three Tonys.)

Over the next few years, these three young men would find time to collaborate on one of the most popular and visionary musicals of our time. Lacamoire first got word of Dear Evan Hansen from director Michael Greif, with whom he had worked years earlier as an audition pianist for Rent. The call from Greif came a few months after Lacamoire’s dinner with Paul; not long after that, Paul was sitting at the piano in Lacamoire’s home office, playing early versions of songs that theater fans would eventually learn by heart.

“He played me ‘Waving Through a Window,’” Lacamoire recalls. “He played me ‘If I Could Tell Her,’ and ‘Only Us’ — all these amazing songs — and I was hooked right away. Because every song he played, I thought, ‘This is beautiful, this melody is totally catchy.’ It all sounded like pop music in a theatrical context, which is the hardest thing to do. My wife was in the other room, and after Justin had left, she was like, ‘Babe, what was that? Whatever that is, you have to work on it.’”

Lacamoire took her advice, and Dear Evan Hansen went on to win multiple honors and multitudes of hearts with its story of a lonely teenager who learns both the dangers and the necessity of connection in our digital age. Now, three years into its Broadway run, with a national tour in its second year, the musical is currently in previews in London, where it’s set to open November 19.

From the beginning, Lacamoire says, he was “taken with the specificity of the music, the quality of the music. There was an aching, and an immediate accessibility, because all the songs are very succinct, very polished, in the best possible way, with tons of heart.” Early in the workshop process, Paul played piano as Pasek sang the numbers. “We dipped our toes into the water together. It’s a very intimate relationship, if you think about it, because writers are presenting brand-new creations, leaving themselves vulnerable. Eventually, I would offer arrangements and orchestrations; it was an additive process.”

One of the first developments was to add an acoustic guitarist, Justin Goldner, to the mix, “because it was clear that’s how Justin [Paul] and Benj were hearing a lot of the songs. That allowed me to be at the piano, using my left hand to play bass and my right hand to add textures and sounds. That was a great way for me to show them, ‘Hey, maybe the piano can do this, and maybe the bassline would do that.’ And they could say, ‘Hey, that’s great,’ or, ‘Let’s try this instead.’ Then we added a drummer and a second keyboard player, and that allowed us to try more things.”

Taking the show on the road two years ago provided a fresh opportunity, Lacamoire notes. “You’ve already gotten a chance to troubleshoot and try things, and a sense of what works and what can be improved. It’s also helpful that the show has been around long enough that people have an awareness of it, from the cast album and YouTube performances, so they have a sense of the style of the show and how it sounds. And it’s always fun to hear new musicians interpret the music, and to add new actors to the family. That means our story is growing.”

In London, he reports, “the first preview was packed with fans. You could just see from the energy in the room, and all the T-shirts and the merchandise. When the lights come up and you see Evan at his laptop, that got applause right away. The audiences have been listening really intently, and they seem to be moved by the same things they’re moved by in the States. They might be a little quieter, maybe whoop a little less, but it’s really resonating with them.”

Not that Lacamoire has stopped giving notes. “There’s no such thing as a perfect show,” he contends. “When I was conducting for Hamilton, I would always aim to have a perfect show, but there was always something that I would attempt to do better the next time. It’s your job to try to steer people in the direction of a certain vision.” But, he adds, “as you bring in new talent, you’re not trying to force people to do something exactly the way you describe it. You have to allow them to bring their best selves to the music and the characters and the story. You try to leave room to be surprised, to have them do something you hadn’t expected.”

And Lacamoire remains eager to bring new energy to a work he continues to cherish. “I’ve been working on this show since 2012 or 2013, and I’m still not tired of the songs,” he says. “They make you feel like you’re being lifted, and you don’t land until the piece is over, so you go through an entire journey with a beginning, a middle, and an end. The songs take you on a ride, and you surrender to it. It makes me proud of the work we put into it, and I still feel hugely invested in the show and in making sure the songs sound the way they’re meant to be heard.”