NEW YORK • In autumn 2016, author Ian McEwan found himself in an unlikely spot: a seaside village on the southern coast of England, in rehearsals with a film director and two young actors.

The director was Dominic Cooke, the actors were Saoirse Ronan and Billy Howle and the film was On Chesil Beach, based on McEwan's 2007 novel and for which he had written the screenplay.

The movie, which debuted at the Toronto International Film Festival in September, was released in the United States one week ago.

McEwan, 69, is no stranger to having his work adapted for the screen. Five of his novels have been made into films, ranging from The Comfort Of Strangers (1990) to Atonement (2007).

But this time, he was not expected to stay away from the location shoots.

"Films are, by convention, a director's medium," McEwan said in a recent interview. "The screenplay writer can often find himself in an awkward position in the process.

"You might generate all the material - scenes, characters, plot-but you find yourself fairly low down in the pecking order once the filming begins. No one wants you around."

On this occasion, he was working with the director to answer the actors' questions on the characters they would play - Edward and Florence, a newly married and sexually inexperienced couple in 1962 - and explaining the repressed era during which the action was set.

Ronan said: "There was no one better to have with us during that time. We had a limited amount of time to develop and discuss the characters' relationships and dynamics before the shoot began, so Ian being there to answer any questions we had was fantastic.

"He was also open to our interpretations of the characters and wanted this to be as much of a collaboration as possible."

McEwan said the rehearsal period helped him to refine his screenplay.

Hearing the actors speak his lines made him realise "that less is more - and so I would take out things here and there".

Cooke found McEwan a wary partner at the beginning of the process when producer Elizabeth Karlsen suggested the two of them meet.

At that point, the script had been around for about five years, with Sam Mendes originally attached as director. "He went off to make two Bond movies," McEwan said.

"Ian was quite cautious," Cooke said. "Not so much because of me, I don't think, but because five years had passed since he first wrote the screenplay and a couple of other directors had come and gone.

"My guess is that he thought, 'Until I know this is really happening, I'm going to hedge my bets.'"

But that meeting went well. Over lunch at the Charlotte Street Hotel, in central London, the two discussed their mutual passion for classical music.

"I was convinced that someone who came in without a deep love and understanding of classical music would quickly be telling me that we had to make Florence into a pop star," McEwan said.

"Dominic was reassuring on that point. We were off and running pretty quickly after that," he added

Cooke agreed that his background in theatre was an easing factor in their working relationship.

"I'm used to that dynamic of having a writer alongside me," he said. "It doesn't mean you don't challenge them. It doesn't mean that you don't occasionally try to make them think differently about what they have written.

"But you are starting from a place of faith, really.

"I found Ian remarkably collaborative, especially for a novelist, which can be a solitary undertaking."

That relationship even extended to casting, with McEwan being the first to raise the idea of Ronan playing Florence.

Ronan, at age 12, had played Briony in the 2007 adaptation of Atonement (for which she received the first of her three Oscar nominations, the others being for Brooklyn in 2016 and Lady Bird this year) and the two had stayed in touch.

"I wanted her from the beginning," McEwan said. "And when I mentioned her to Dominic, he was excited."

The five-year delay in production turned out to be an asset.

"The screenplay languished and I moved on to other things," he said.

"And there was a great fortune in that. Because when I started, Saoirse was probably in her mid-teens and in no position to play such a part.

"But by the time Dominic and I began to work on the project, we had both seen and loved Brooklyn (about a young Irish woman in the United States), in which she was brilliant."

Ronan is now 24.

McEwan said: "And I thought, 'Well, this is just a magnificent opportunity.'"

NYTIMES