‘Once’ at John W. Engeman Theater in Northport

“It was terrifying,” says Barry DeBois, of the first time he stepped in front of a live audience as Guy in a national tour performance of the Tony Award-winning musical “Once.” “You’d be surprised how little onstage rehearsal time the understudy gets.”

Now well-seasoned in the role of the nameless Dublin busker who attracts a young immigrant flower seller and musician (aka Girl) with his songs, DeBois, 35, is the lead Guy in the film-turned-musical production currently playing at John W. Engeman Theater in Northport.

STAGE BAND

With the absence of a pit orchestra, the musicianship of the actors, who provide the instrumental accompaniment directly onstage, is exceptional. “It’s taken a lot of practice,” says DeBois, who had previously amped up his high school band guitar-playing skills for an off-off-Broadway performance of “The Wedding Singer.” “One of my favorite moments is when we sing ‘Gold,’ the song that closes out Act 1, and everyone is playing, moving and singing together. It gives me chills.”

Audiences might be similarly moved when the tenor and Andrea Goss, the actress who plays Girl and was previously the Broadway understudy for the part, perform the showstopping closing number. “Falling Slowly,” which won an Academy Award for best song in the film, was inspired by the real-life romance of the movie version’s stars and the ballad’s authors, Irish rocker Glen Hansard and Czech singer Markéta Irglová. “When I sing the song, I always look up to the balcony where I sat when I saw Glen performing live and give a nod to whomever is sitting there,” DeBois says.

AN OFF-FORMULA MUSICAL

Just as the musical staging of “Once” is unconventional, so too is its love story. While most musicals embrace the age-old formula boy meets girl, boy loses girl, boy gets girl, the romance between Guy and Girl does not follow the classic narrative. “ ‘Once’ takes old story tropes and turns them on their head,” says DeBois of the show not having — beware, spoiler alert — a Hollywood happy ending. “It is not the same old story. It feels real. There’s grit and life’s complications.”

While some people may be disappointed with “Once’s” bittersweet resolution, it resonates with DeBois, who left his career as a mechanical engineer to pursue his passion for the stage. “I leave hopeful. At the beginning, both of the characters are stuck, but by the end they are on their way to adventures,” he says. “And I think that’s beautiful.”