American musical theater changed when Stephen Sondheim began writing musicals that explored the trajectory of a character’s inner life rather than following an action-driven plot with its strings of dancing girls and its requisite happy ending. Doubtless having Sondheim’s example in mind, singer-songwriter Melissa Manchester and playwright/lyricist Jeffrey Sweet found rich material for their first musical collaboration in Welsh writer Bernice Rubens’s poignant novel I Sent a Letter to My Love, which had already been transformed into a French film, Chère inconnue, in 1980.

The musical is set in rural Maine, circa the 1950s, where the aging Stan and his sister, Amy, live together in a small house by the side of a lake that they never cross, despite the presence of a resort, with its lights and music, on the other side. Amy made the trip once when she was 17, falling in love with Jimmy, the singer with the band. He seduced her and then, after an intense two-week affair, left town, never to write or return.

Jimmy is the third character in the cast of five, a dream figure who serves as a cynical voice of reason, heard and seen only by Amy and the audience. She conjures him up for comfort, commenting that he never ages. Stan, who calls himself a cripple (he’s been locked in a wheelchair since a childhood bout with polio), leads a fantasy life of his own, complete with Playboy-type photographs of women tucked beneath his mattress. In a correspondence with a pen pal who put a blind ad in the local paper, he pours out his longings, not realizing it’s his sister on the other end. Amy, who knows what’s up, gets off on writing love letters to him — as much for the thrill of the new experience as to fuel Stan’s illusion. But the issue of incest lurks only at the edges of the story: these are sweet-natured siblings who care for each other, and David Garrison (best known as Steve on TV’s Married . . . with Children) and Cass Morgan infuse their roles with pungent feeling. And Kevin Earley as Jimmy delivers a convincing period lilt to his signature song, " Perfect Timing. "

The agent of change is Gwen (played with comic verve by Bethe B. Austin), a single lady of a certain age who has come to rent the cottage on the siblings’ property: she gives Stan both his physical and emotional release and frees Amy along with him. The final character, Miss Morgan, is a teacher with amateur acting skills who’s hired to impersonate Stan’s correspondent. Diana Canova gives the character a surprising complexity and also delivers a perky rendition of the country-music number " The Day I Met My Friend. "

Patricia Birch, the choreographer of the original production of Grease, directs the small-scale work with a becoming decorum, solving the problem of filling a huge arena stage with only a quintet of characters trapped by self-imposed boundaries. Scenic designer James Morgan opens up the physical setting by providing a hanging circumference of picture-postcard scenes of the lake that twinkle with tiny lights at night.

Manchester’s score is as much recitative as a series of songs, with Amy’s heart-rending entreaty, " Lady Seeks Gentleman, " sure to become a staple on the cabaret circuit. Sweet’s lyrics are less satisfactory, relying too much on bland adjectives like " nice " and ‘lovely. " But Manchester and Sweet can be forgiven if the outcome of their musical is more optimistic than reality would suppose, since they’ve found a compelling world to map within these ordinary lives.