NEW YORK, June 28 (UPI) — Once and Sing Street writer-director John Carney’s new music dramedy, Power Ballad, explores how one hit song completely changes the lives of former boy band member Danny (Nick Jonas) and struggling wedding singer Rick (Paul Rudd).

Peter McDonald co-wrote the film and plays Sandy, Rick’s band-mate and loyal best friend, who stands by him when he claims he helped write one of the most famous songs in the world.

The movie is now playing in theaters and available on pay-per-view platforms.

“This is one of the themes of the story — what do you define as success for yourself and what would you do to achieve it?” McDonald, 54 told UPI in a recent Zoom interview.

“One of the saddest moments in the film, for me, when we were writing it was Rick’s personal life is crumbling and his professional life is crumbling. But he says to Dan: ‘I even stopped making music because I can’t write because of what’s happened. It left quite a bad taste [in my mouth] in relation to the one place where I expressed myself more clearly than anything else,'” he explained.

“That’s what the movie is — that utility of your passion and your art, what it brings to your life.”

The film also looks at how the intersection of creativity and commerce, and what moral and legal obligations artists have to each other when they collaborate.

“We didn’t want to have a Danny who was a villain,” McDonald said.

“He’s at a juncture where he’s either going to sink or swim,” he added. “He’s either going to remain relevant in the very fickle world of music or he’s probably going to become a has-been and he’s too young and vital and talented for that to happen to him.”

The casting of Jonas, an affable, real-life pop star, was important because the audience is supposed to see Danny as a musician in a rut not a heartless thief.

“He’s trying to survive and the decisions he makes in the movie are in service to that, so, hopefully, we can see it from his point of view, as well, and how, in many ways, you can be guided by those ambitions, but, at the same time, acknowledge Rick’s song is a kind of half his song.”

The film shows Rick initially trying to get in touch with Danny through professional channels to see if he will pay him something for his contributions to the song, then angrily confronting him at a party after Danny’s representatives rebuff him.

“Those two guys got it,” McDonald said of how Rudd and Jonas played the more intense, emotional moments they shared.

“They’re great actors. They really cared for the script. They both came on board very quickly when they read it. They both loved John’s films,” he said.

“We were doing that scene and, right way, they went at each other from the word, ‘Go,'” he laughed, noting it was difficult to get them to pretend to be mad at each other.

“If anything it was trying to get them to calm down a little bit, so we could understand what they were saying.”

Always having Rick’s back is Sandy, a man who doesn’t need to play Madison Square Garden to feel happy and fulfilled.

“He doesn’t need to be called a rock star because he became a rock star the moment he picked up an electric guitar. Music is his life. It’s his bread and butter and, as long as he’s allowed to do that, to make some kind of living out of it, he’s brilliant,” McDonald said.

“Somebody who can see the world with such freedom of spirit can also see it quite simply and, in many ways, in these complicated situations, the solution to them is quite simple. And you need friends like that in life.”