But the movie never felt quite like the novel had come to life, McCauley said — not that time, and not with some of his later books that were adapted into films in France.

“In each case, I often feel like the book is mine, but the movie is the screenwriter’s or the director’s,” he said. “It’s as if the film is inspired by my work, rather than actually being my work.”

Now McCauley is having a different kind of experience in seeing characters take three-dimensional form, after trying his hand at writing plays. He and his partner, Sebastian ­Stuart, have penned a handful in the past few years, and one of them, “Where There’s a Will,” will be performed this weekend in Brookline by the Freelance Players, a youth theater troupe that draws young actors from communities around Greater Boston, including Arlington, Brookline, Lincoln, Millis, Needham, and Newton.

“It’s really fun to write something for kids,” said McCauley, whose six published novels are all aimed at an adult audience. “You can make it a little bit more extreme and crazy than you would for adults. At the same time, we strive to maintain a thematic integrity, and also to toss in a little lesson along the way.”

McCauley also wrote the lyrics for “Where There’s a Will.” Brookline resident Narcissa Campion set his words to music. All of this makes for a very different process from writing a novel, McCauley said.

“Playwriting is tremendously collaborative, especially when Sebastian and I work together,” McCauley said of the relationship that is both a business and domestic partnership.

“We kind of act it out as we’re writing it. And then working with the director and actors adds a whole new layer of collaboration. Whereas novel writing is totally solitary, for me anyway. It all happens in your head, which is both pleasurable and maddening. You never expect to see it acted out, and even if a novel becomes a movie, it doesn’t feel like quite the same work.”

Although the young performers in the Freelance Players production may not realize quite how unusual it is to be working with a writer of McCauley’s stature, many of them appreciate the benefits of participating in an original production.

“When you do a school play that everyone knows, like ‘Fiddler on the Roof,’ it’s a different experience,” observed Raavi Malik, an eighth-grader from Arlington who has two roles in “Where There’s a Will.” “But I really like being in original plays where the audience finds out what happens as the play unfolds, rather than knowing beforehand just what’s going to happen.”

For Noah Weisskopf, from Newton’s Waban section, there’s a more practical benefit to having the lyricist and composer both on site during rehearsals.

“It allows you to make changes if you need to,” he said. “If you’re finding it difficult to sing a particular phrase, the person who wrote the song can change it for you. It allows everyone to be more creative. When you’re in a play you’ve never seen before, playing a character you’ve never seen before, you can do it any way you want; you have the ability to make it your own.”

It is just this kind of creativity that Kippy Dewey, founder of the Freelance Players and director of “Where There’s a Will,” tries to bring out in every production.

“It’s an incredible luxury to have material written for our group,” Dewey said. “Stephen was very involved in our process. He works right alongside us, rewriting roles, shortening, tightening, getting rid of things that don’t work. It’s a wonderful experience for young actors to see this process take place. Kids who like to act will have plenty of opportunities to be in the Broadway classics. But having these characters be their own, getting to create them for the first time, with these writers, is a remarkable opportunity.”

And for McCauley, it may be the start of a new direction for his career; he was recently asked by a New York producer if he would adapt one of his short stories into a play.

“When you’re sitting in the theater watching your own work be performed, you get to see people’s reactions immediately,” said McCauley. “Unlike with a book, you don’t have to wait for responses. That’s very satisfying. Unless it’s a joke that falls flat.”