Catherine Doherty and Brett Schrier had worked together on a few musicals at Northern Stage when the banter that goes along with life in the theater turned into something more serious: an idea for a play.

In the car on the way to casting calls in New York and during rehearsal breaks, Doherty, the White River Junction theater company's producing director, and Schrier, musical director for Northern Stage productions of Cats and Les Miserables, among other musicals, started extemporizing bits of songs.

“Are you writing this down?” Brooke Ciardelli, the company's founder and artistic director, often asked them.

Eventually, they did start writing things down, and for the next few weeks, Upper Valley theater-goers can experience that rare article, a musical written in their midst. Take Two, with book and lyrics by Doherty, music by Schrier and direction by Ciardelli has a final preview tonight and opens tomorrow night at the Briggs Opera House in White River Junction.

The two-act musical was not only a labor of love for its two writers, but also an example of how a community that values creativity can nourish a project to adulthood, Ciardelli said. And since it was crafted with a theater niche in mind -- the affordable-to-produce musical -- Take Two might have a healthy life beyond the Northern Stage production.

The play follows four people navigating the emotionally perilous waters of second love. Two of the characters are a recently separated and soon-to-be-divorced couple. The other two characters are the older couple's recently widowed daughter, and her co-worker, a man getting a divorce and coming to terms with his homosexuality. The show is set in the present day, and the characters go about looking for love with all the devices of modern communication at their disposal.

That wasn't quite how the writing started.

“What was the first title that I said?” Doherty asked Schrier during an interview this week. “Boomer,” he said. The play was going to be called Boomer: The Baby Musical, and have song titles like Papa Is a Rolling Stone, 401(k) and Supplement Yourself. But that idea went by the boards. The first song Doherty and Schrier wrote together, Second Soul, about trying to find another soulmate, became the backbone for Take Two.

“I think we knew what kind of show we wanted,” Doherty said, but they “didn't know what it consisted of.”

For example, should all the characters be the same age, as in I Love You, You're Perfect, Now Change, which Doherty and Schrier worked on together a few years ago? Would it be a sketch musical without a narrative thread, or a more traditional, and more difficult to write, book musical? What sorts of voices did they want to write for?

Even as they wrestled with these fundamental questions, Ciardelli said she knew what the outcome would be.

“I was utterly convinced that they were going to write a musical,” she said. Doherty said that despite a long career in theater and film, writing a musical wasn't something she'd ever considered. “Not in a million years,” she said.

The early creative process the team described sounds like skylarking. Doherty recorded some of the early ideas for one song, 60 Is the New 40, on her voice mail from her cell phone during a New York cab ride with Schrier and Ciardelli. The cell phone was an appropriate tool for a play featuring songs with such titles as You Can't Judge a Profile by the Picture and Just Hit Send. The two-hour show now comprises 14 full musical numbers, and a total of 33 musical pieces, including transitions and prologues.

The characters Doherty and Schrier settled on were people “who for some reason or another have lost their true love,” Doherty said. “They just sort of emerged.”

Starting last May, the two developed their work in a series of six retreats at homes of Northern Stage supporters in Woodstock and in Randolph, N.H., homes with beautiful views that Doherty and Schrier barely saw as they wrote songs, note by note and word by word. As the retreats went on, Ciardelli watched the writers change with their task.

“The show was starting to have a life of its own,” and serving the needs of the show was more difficult than writing individual songs, she said. Doherty estimated that a third to half of the songs were written before work began on the book, the spoken story of the play. Ciardelli said Doherty and Schrier would come back to work from their retreats “exhausted.”

“It requires such an intense focus and concentration,” Doherty said. One of the songs took them 18 hours to write, she said.

But there were encouraging signs along the way. Rising Broadway star Mara Davi sang Second Soul in cabaret performances in Manhattan last year.

“It was very exciting to hear that from a woman who has the instrument that she has,” Doherty said.

The show took a leap forward in an August workshop with four singers, an accompanist and a music copyist.

“I would say 50 percent of the show changed since the workshop,” Schrier said. “We needed to focus some attention on the arc of the characters.”

In addition to writing a show about modern love, Doherty and Schrier wanted to craft a play that would appeal to theater companies in search of a musical that would be relatively easy and inexpensive to produce.

“I started to think about how Take Two can be marketed in the musical theater world,” Schrier said. “You think about things like how performable is it, how producible is it.”

The play speaks to a wide range of people, can be performed on any type of stage and can be accompanied by just a piano on the stage or by a small orchestra, Schrier said. A four-person musical is likely to be very appealing to theater companies in the current economy, he noted.

The result, Ciardelli said, holds its own with the other plays in the season, including works by Neil Simon and Tennessee Williams, Ciardelli said.

“Every audience member leaves feeling changed in some way,” Schrier said.

The proof of that arrives this week. Ordinarily, the writers of a new musical would package up the book and music with a CD and send it out to theaters and publishers. The best many can hope for at first is to hear the work on stage in a reading and sing-through.

Northern Stage is spending around $100,000 to develop and produce Take Two, but the generosity of the company's friends and donors added up to far more. To produce the show, Northern Stage needed a grand piano. Rental was out of the question, Ciardelli said. “We had three different people say, ‘You can take the piano out of my house.' ”

“It's extraordinary.”

Northern Stage presents “Take Two” at the Briggs Opera House in White River Junction, through May 17. Ticket prices range from $36 to $71 for adults and from $34 to $69 for seniors and youths. Call (802) 291-9009 or got to www.northernstage.org for tickets and information.