There is a blunt bit of foreshadowing early on in the deftly staged production of the musical “John and Jen” that just opened at Swift Creek Mill Theatre.

As 6-year old Jen (Nicole Pearson) sings “Welcome to the World” to her infant brother, she explains that “the people who you’ll love the most / Are also the ones who make you cry.”

As that brother, John (Malcolm Holmes), grows up, the siblings forge a fiercely interdependent bond that seems built to last. Instead, the complications of life start to shred it, causing tears, heartache and complications across generations.

The first act ends with the siblings’ connection shattered by tragedy. The second act starts years later with Jen, now a single mom, establishing an even more codependent bond with her son, also named John (and also played by Holmes). The biggest question the show poses is whether Jen will sabotage this new relationship by overcompensating for previous mistakes or succeed in transcending her past.

Director Tom Width sets the musical in the family attic, where the growth of the siblings’ relationship is represented in the accumulation of artifacts from their lives. As the story progresses from 1952 to 1990, actors easily swap costume pieces from the attic’s clothes racks to indicate their characters’ aging.

Costume designer Maura Lynch Cravey has made astute selections to represent the passing of time, from John’s boyish play clothes to the bold outfit Jen sports in her hippie-dippie 1960s phase.

The responsibility for believably carrying “John and Jen” through these transitions falls squarely on Pearson and Holmes. The actors both succeed admirably and their performances are the principal reasons to see this show.

Pearson shows off her muscular vocal prowess early on in “Welcome to the World” as well as her pep talk to young John, “Think Big.” Holmes has his first moment to shine in the playful “Trouble With Men,” a litany of Jen’s pattern of serial dating through her teen years.

Neither actor overplays their characters’ childishness in the early scenes and Holmes, in particular, shows a dexterity in projecting emotional nuance in his singing voice.

But even as the actors successfully project subtlety where they can, the show seems intent on flattening their roles to be as one-dimensional as possible. “John and Jen” was the first show written by composer Andrew Lippa (in collaboration with Tom Greenwald), who would go on to write “The Wild Party” and was nominated for a Tony Award for writing music and lyrics for “The Addams Family.”

This show reflects an artist still mastering his skills early in his career. By depicting them over such a long stretch of time, Jen and both Johns never seem fully fleshed out, largely reduced to the kind of mannered reactions to circumstances that a sung-through musical format already exacerbates.

The storyline also uses intimations about an abusive parent as a wedge to separate the characters without giving the issue any real heft.

“John and Jen” shines when it gets specific, such as a lyric that describes becoming aware that you loathe someone when “you get this taste in your mouth, like tomatoes.” The show totally breaks format for the song “Talk Show,” wherein John and Jen argue the reasons for their emotional distress in Dr. Phil-style talk show segments. While the scene is great fun, it also demonstrates how easily the show’s conflicts can be summed up in self-help platitudes.

Still, there is plenty to enjoy here, with an outstanding band (led by music director Paul Deiss) delivering sparkling renditions of Lippa’s somewhat forgettable melodies. Joe Doran’s lighting design is so good it generates laughs of its own, specifically in a baseball-centric scene later in the show.

If nothing else, “John and Jen” provides two excellent actors with a rich palette to exercise their abundant skills. Their big finale, “Every Goodbye is Hello,” is filled with squishy sentiment about “wonderful things” and “a magical phrase,” but Holmes and Pearson perform it with so much gusto and vitality, you forget the superficiality and just enjoy the exhilarating sounds.

“John and Jen” is playing at Swift Creek Mill Theatre, 17401 Route 1 in South Chesterfield, through Sept. 28. Tickets and information available at https://www.swiftcreekmill.com/.