Sometime in the 2000s, the producer Lindsay Doran asked her doctor for a book recommendation. “I’m reading that book everybody’s reading,” the doctor replied. “You know, the one about the shepherd who’s murdered and the sheep solve the crime.”

Doran had not heard of the book, “Three Bags Full,” a best-selling novel by a German graduate student (“No one’s reading it,” she recalls responding, inaccurately), but she was struck by what sounded like an irresistible elevator pitch. “Everything came together for me in that one sentence,” she said. “The fact that it was sheep rather than some other animal felt so resonant.”

Doran spent years trying to extricate the book from a complicated rights situation, and years more turning it into a movie. The result, opening Friday, is “The Sheep Detectives,” which features Nicholas Braun and Emma Thompson as humans, and Julia Louis-Dreyfus, Patrick Stewart and others giving voice to C.G.I. sheep stirred from their customary ruminations by the death of their shepherd, George (Hugh Jackman).

The film, rated PG, is an Agatha Christie-lite mystery with eccentric suspects, a comically bumbling cop (Braun) and a passel of ovine investigators. It’s also a coming-of-age story about growing up and losing your innocence that might have a “Bambi”-like resonance for children. The movie’s sheep have a way of erasing unpleasant things from their minds — they believe, for instance, that instead of dying, they just turn into clouds — but learn that death is an inextricable part of life.

“In some ways, the most important character is Mopple, the sheep played by Chris O’Dowd,” the screenwriter, Craig Mazin, said in a video interview. “He has a defect — he does not know how to forget — and he’s been carrying his memories all alone.”

“Three Bags Full” is an adult novel that includes grown-up themes like drugs and suicide. In adapting it for a younger audience, Mazin toned down its darker elements, changed its ending, and — for help in writing about death — consulted a book by Fred Rogers, TV’s Mister Rogers, about how to talk to children about difficult subjects.

The journey from book to film has been long and circuitous. “Three Bags Full” was written by Leonie Swann, then a 20-something German doctoral student studying English literature. Distracting herself from her unwritten dissertation, on the topic of “the animal point of view in fiction,” she began a short story “playing around with the idea of sheep detectives,” she said. “And I realized it was more like a novel, and it wasn’t the worst novel I’d ever seen.”

Why sheep? “I wasn’t someone who was thinking about sheep all the time,” Swann, who lives in the English countryside and has a dog named Ezra Hound, said in a video interview. Yet they have always hovered on the periphery of her life.

There was a friendly sheep that she used to see on her way to school. There was an irate ram that once chased her through the streets of a Bavarian village. And there were thousands and thousands of sheep in the fields of Ireland, where she lived for a time. “There were so many of them, and you could tell there was a lot of personality behind them,” she said.

A book in which sheep are stirred to action had to be a mystery, she said, to motivate the main characters. “In a lot of other stories, you would have trouble making a sheep realize there’s a story there,” she said. “They would just keep grazing. But murder is an existential problem that speaks to sheep as well as humans.”

Swann (the name is a pseudonym; she has never publicly disclosed her real name) found a literary agent, Astrid Poppenhusen, who brought her manuscript to market. Published in 2005, the book was translated into 30 languages and ended up spending three and a half years on German best-seller lists. (The German title is “Glennkill,” after the village in which it takes place.) Other novels followed, including a sheep-centric sequel, “Big Bad Wool,” but Swann never finished her dissertation.

Doran, the producer, read the book — now published in the United States by Soho Press, along with four other Swann novels — soon after hearing about it. She was determined to make it into a movie. Whenever she told anyone about the idea, she said, she had them at “sheep.”

The director, Kyle Balda (whose credits include “Minions”), was so excited when he first read the script, in 2022, that “I immediately drove out to a sheep farm” near his house in Oregon, he said in a video interview. “Very instantly I could see the behavior of the sheep, their different personalities. I learned very quickly that there are more varieties of sheep than dogs.”

How to make the sheep look realistic, and how to strike the proper balance between their inherent sheep-iness and their human-esque emotions were important questions the filmmakers grappled with.

It was essential that “the sheep in this world are sheep” rather than humans in sheep’s clothing, Balda said. “It’s not the kind of story where they are partnered with humans and talking to each other.”

That means that like real sheep, the movie sheep have short attention spans. They’re afraid to cross the road. “They don’t drive cars; they don’t wear pants; they’re not joke characters saying things like, ‘This grass would taste better with a little ranch dressing,’” Doran said.

And whenever they speak, their words register to humans as bleating, the way the adult speech in “Peanuts” cartoons sounds like trombone-y gibberish to Charlie Brown and his friends.

Lily, the leader of the flock, is played by Julia Louis-Dreyfus. It is not her first time voicing an animal in a movie: She has played, among other creatures, an ant in “A Bug’s Life” and a horse in “Animal Farm.” “When I read the script, I thought, ‘Wow, this is so weird,’” she said in a video interview. “It’s not derivative of anything else.”

Lily is unquestionably not a person; among other things, like a real sheep, she has a relatively immobile face set off by lively ears. “But her journey is a human journey where she realizes certain things about life she didn’t understand,” Louis-Dreyfus said. “There’s also the question of being a leader, and how to do that when you’re questioning your own point of view.”

Nicholas Braun took easily to the role of Officer Tim, the inept constable charged with solving the shepherd’s murder.

“The part was a little Greg-adjacent in the beginning, and I don’t really want to play too many Gregs,” Braun said via video, referring to Cousin Greg, his hapless punching bag of a character in the TV drama “Succession.”

“I’m post-Greg,” he said.

It takes Officer Tim some time to notice that the neighborhood sheep might be actively helping him tackle the case. But Braun said that unlike Greg, who is stuck in perpetual ineptitude, Tim gets to grow into a braver and more assertive person, a take-charge romantic hero — much the way the sheep are forced into action from their default position of “just forgetting about it and moving on and going back to eating grass,” he said.

Braun mused for a bit about other potential animal detectives — horses, say, or cows — but concluded that the sheep in the film were just right for the job. He predicted that the movie would change people’s perception of sheep, much the way “Toy Story” made them “look at their toys, or their kids’ toys, differently.”

“I don’t think people are going to be eating as much lamb after this,” he said.,