British filmmaker talks about ‘pain and rage’ in an American town in ‘Three Billboards Outside Ebbing, Missouri’

It was a bus trip through America 20 years ago that gave the British/Irish playwright and filmmaker Martin McDonagh the inspiration for his new movie, “Three Billboards Outside Ebbing, Missouri.”

“I saw something on a couple of billboards that was very similar to what was on our billboards [in the movie],” McDonagh said in a phone interview.

In the movie (which opens Wednesday in Salt Lake City), a woman in a small town, Mildred Hayes (played by Frances McDormand), rents three billboards on the road into town. The message is a pointed call to the town’s police chief, Bill Willoughby (Woody Harrelson), to make an arrest in the rape and murder of her daughter seven months earlier.

The real billboards, somewhere in the Deep South, were “as stark and as dreadful as our message,” McDonagh said. “It stuck in the back of my mind for years, the idea of what kind of pain and rage would prompt a message like that.”

“Three Billboards Outside Ebbing, Missouri” is in some ways different from McDonagh’s previous movies, both crime thrillers with dark comic streaks: the 2008 gangster film “In Bruges” and the 2012 hitman comedy “Seven Psychopaths.”

“I really wanted to write a strong female lead for a film, because I hadn’t really done that in my previous two films,” McDonagh said. Once he had the seed of Mildred’s character, things grew “really organically. I didn’t plot the film at all. I knew she was completely strong and fearless and intelligent and had a sharp sense of humor.”

Mildred’s pain is something McDonagh thinks is universal. “Life does go on, unless you’re at the center of that pain and that tragedy,” he said. “She’s raging but there’s no person that really is in the wrong. There’s rage at ineptitude, but it’s really impossible to solve.”

On the other side, he said it was important “to make the cops, and certainly Woody’s character, not the enemy. In some ways, it’s about two good people going to war with each other. … The idea is that there are no full-on heroes and no full-on villains in this.”

As McDonagh wrote the script, he did what the pros say a writer should never do: He wrote with a specific actor — in this case, McDormand — in mind.

“I had her voice in my head as I was writing the part,” he said of McDormand, who’s being talked about as a leading contender to earn her second Academy Award. (Her first was for “Fargo.”) “Once I was done, I was really hopeful she wouldn’t turn it down. We sent it to her…, and she said yes, pretty straightaway. There’s no one else who could have done it. … I would have been screwed if she had said no.”

McDonagh also relied on what’s becoming his own repertory company. Harrelson appeared in “Seven Psychopaths,” as did Abbie Cornish (who plays Willoughby’s wife), Zeljko Ivanek (who also appeared in “In Bruges” and the Broadway production of McDonagh’s play “The Pillowman”) and Sam Rockwell (who was in “Seven Psychopaths” and the play “A Behanding in Spokane”).

“It means you’re not working with a brand-new actor, you’re working with an old friend, almost,” he said. “It feels like family.”

Rockwell’s character, a racist and not-too-bright cop under Willoughby’s command, is pivotal to the story, and McDonagh can’t imagine anyone else playing him.

“He’s not scared of going to the darker places without sentimentalizing them,” McDonagh said. Also, Rockwell has “a great sense of humor. There’s always a kind of twinkle in his eye in every character he plays.”

With “Three Billboards Outside Ebbing, Missouri” making its way in the world, McDonagh is turning his attention back to the stage. His play “Hangmen,” which he premiered in London in 2015, will make its Broadway debut in January, and he’s writing another play in the works for a London unveiling next year. Another movie may not be in the offing for another two or three years.

And McDonagh keeps his stage and screen careers separate. He vows never to make a movie version of one of his plays.

“I’m dead-set against that. That’s never, ever going to happen,” he said. “You kind of have to be true to the medium that you’re writing a story for.”