UNEXPECTED JOY

Presented by Wellfleet Harbor Actors Theater. At the Julie Harris Stage, 2357 Route 6. Wellfleet, through Aug. 20. Tickets: $12-$50, 508-349-9428, www.what.org

Lyricist Bill Russell and composer Janet Hood’s collaborations have yielded five musicals over as many decades. A professional partnership that began when both were college students blossomed in Boston in the 1970s and has evolved into a near-lifelong friendship that every so often produces musical theater.

Boston is still home to Hood, who lives in West Roxbury. Russell, a Tony nominee for 1997’s “Side Show,’’ lives in New York. That’s where the pair was recently rehearsing their fifth musical, “Unexpected Joy,’’ which is having its world premiere at the Wellfleet Harbor Actors Theater. The show runs through Aug. 20.

Hood, an accomplished pianist who for many years played keyboard in the orchestra pit when touring shows came to Boston, was apprehensive when Russell asked her to write the music for “Unexpected Joy’’ because she hadn’t composed a musical with him since 1989’s “Elegies for Angels, Punks and Raging Queens,’’ about the AIDS epidemic. But Russell had no qualms at all.

“I knew she was absolutely the right person for this. I’d been thinking of a musical about family members with different styles of music, like John Raitt and Bonnie Raitt,’’ he says. Another point of inspiration came when a friend, who’d been married to her husband for 30 years, decided to convert to Judaism, fell in love with a woman rabbi, and ended up leaving her husband for her.

“Unexpected Joy’’ is about three generations of women singers. Joy (Sally Mayes) is a baby boomer who was once part of a popular duo called Jump and Joy. As Joy organizes a memorial concert in Provincetown for the late Jump, who was a romantic as well as musical partner, she’s joined by their daughter, Rachel (Michelle Duffy), and Rachel’s daughter, Tamara (Charity Farrell), an aspiring rocker. But Joy has another reason for the celebration: She plans to get married to her activist girlfriend, Lou (Lacretta Nicole), but hasn’t told her family yet.

For Hood, the show’s autobiographical qualities were a selling point. “It takes place on the Cape; for several years Bill and I shared a house in Truro, and I’ve performed many times in Provincetown. I really appreciate that the four leads are women and all ages of women,’’ she says, adding that “Unexpected Joy’’ will feature pop, blues, rock ’n’ roll, and a gospel number for Rachel “who’s a born-again Christian who sings on her husband’s evangelical TV show.’’

Russell never doubted that he and Hood could create a vibrant score, but he wondered if the show’s plot had lost its urgency. “We started in 2005 when Massachusetts was the only state that allowed gay marriage. Over the years, I worried that it would be out of date with the rapid change in laws and attitudes,’’ he says. “Then something like [the massacre of 49 people at a gay nightclub in Orlando] happens, and it’s clear these issues are not resolved.’’

“The family dynamics that the show addresses are universal,’’ adds Hood.

In many ways, Hood and Russell’s friendship reflects five decades of LGBT progress. They met in 1969 when Hood, a student at Oberlin College, and Russell, studying theater at Morningside College in Sioux City, Iowa, were both working at a summer resort in northern New Jersey. Russell was directing 30-minute versions of musicals and, with Hood as music director, “we did a short version of ‘Hair’ which was on Broadway at the time,’’ he says. “Janet could do anything. She sight reads incredibly but she also plays by ear so it’s exciting to work with her. ‘Hair’ inspired me to write a rock musical.’’

One of Russell’s Morningside professors, Bill Becvar, was headed to the University of Kansas that fall and told Russell he’d stage the show there.

“We hadn’t even written anything and it was already scheduled,’’ says Russell.

The fledgling songwriters worked furiously from their respective campuses, swapping songs on reel-to-reel tapes through the mail. “Sun, Son,’’ a modern version of the Icarus myth, won the national BMI Inter-Varsity Show Competition for original musicals.

Hood enrolled at Berklee School of Music for her senior year, sharing an apartment with another Oberlin transplant, Linda Langford. Russell “followed her to Boston,’’ he says, and the three friends lived in the same Allston neighborhood and hung out at a bar called Brandy’s, where Hood and Langford often sat in with the band.

“I’d tell them, ‘You’re both so much better than these guys playing with you. You should go out on your own,’ ’’ Russell says. “And they said, ‘We might if you manage us.’ ’’ The duo Jade and Sarsaparilla was born, with Russell writing the songs that Hood and Langford, by now a couple, sang to one another. They played gigs around New England for the next seven years, releasing an album in 1976.

“To this day, Jade and Sarsaparilla is one of the things I’m proudest to have been involved with,’’ says Russell. “It was kind of revolutionary. The first gig was in 1973; Watergate was going on. I came out. Everything was happening so fast.’’

Some five decades later, Hood and Russell are swapping MP3s instead of reel-to-reel tapes, but they’re still spurring one another’s creativity. “We have this very long thread,’’ says Hood. “Now it’s shorthand.’’

UNEXPECTED JOY

Presented by Wellfleet Harbor Actors Theater. At the Julie Harris Stage, 2357 Route 6. Wellfleet, through Aug. 20. Tickets: $12-$50, 508-349-9428, www.what.org

Loren King can be reached at loren.king@comcast.net.