“Regency Girls,” a new musical comedy set in the period of Jane Austen’s novels, begins on a note that fans of “Pride and Prejudice” will savor.

The fate of the Benton family depends on finding husbands for the two oldest daughters, Elinor (Isabelle McCalla) and Jane (Kate Rockwell), both of whom are being courted by wealthy scions. Distress ensues when these savior suitors, who are bound for a yearlong voyage, fail to show up at the appointed hour to bid the ladies farewell. But at the last minute they not only appear but propose, saving the Benton daughters from a fate worse than spinsterhood: family insolvency.

A boisterously vivacious opening number, “A Happy Ending Beginning,” sets the household into ecstatic motion early on in “Regency Girls,” which is having its world premiere at San Diego’s Old Globe. But happy endings aren’t meant to come at the start of romantic tales and the exuberance proves to be premature.

Elinor, who seems modeled on Austen’s Elizabeth Bennet, does something her lively, intelligent and fiercely independent counterpart from “Pride and Prejudice” would never do: She gets pregnant before her wedding day. On the night of their engagement, Elinor and Stanton (a winning Nik Walker) apparently succumbed to their passion, and now that Stanton is at sea with Dingley (Gabe Gibbs), Jane’s horribly snooty fiancé, there seems little hope that Elinor’s situation can be rectified by a rushed wedding.

Jane, far more conventional than her older sister, can only think of how Elinor’s disgrace will ruin her own future. Haughty, hypocritical Dingley, she fears, won’t want anything to do with the family once this scandal goes viral, which in the Regency period translates into a wildfire of whispering throughout polite society.

Elinor finds an ally in her quick-thinking maid, Dabney (Krystina Alabado), who has a handbill listing the services of Madame Restell (Janine LaManna), a London-based midwife who helps women in distress. It’s not immediately clear why Dabney has this advertisement, but Elinor discovers that she doesn’t have to go through this difficulty alone.

Petunia (Ryann Redmond), a married family friend exhausted by pregnancy and motherhood, volunteers to accompany Elinor to London. Jane, anxious to see that her sister’s awkward matter is discreetly handled, agrees to go too. And Dabney, suspiciously eager, insists that she be included, even if she has “to ride atop the luggage.”

Before you know it, “Regency Girls” transforms into a rowdy road trip. Try to imagine “Thelma & Louise” crossed with Austen’s romantic comedy of manners, “Bridgerton” and some naughty sketch comedy, and you’ll have an approximation of the melange the creators are attempting.

The musical’s book, written by Jennifer Crittenden and Gabrielle Allan, TV writers with illustrious comedy credits, trades freely in anachronisms for laughs. The score follows suit, with Curtis Moore’s music and Amanda Green’s lyrics setting up the period flavor only to bust out in Broadway-style pop, rock and even hip-hop.

Regency girls just want to have fun, so why confine them to one particular genre or historical epoch? Put them instead in a slow-trotting carriage and see how far they can go.

The show is both genuinely funny and unabashedly silly, and director and choreographer Josh Rhodes has his hands full reining in some of the sitcom dopiness. This “pre-Broadway engagement” reveals the production’s bright potential. Who could resist a musical comedy road trip celebrating girl power? But the humor grows broader and more ridiculous, as though scripted for a laugh track.

Crittenden and Allan have lively imaginations, but the wild situations they concoct are treated like joke machines. The introduction of Galloping Dick (Gibbs, energetically doing double duty), a Robin Hood-esque Lothario who excites Jane’s romantic interest on the road to London, pushes the zaniness into overdrive.

There are early signs of buffoonery involving a maternal wig. And a cartoonish note is struck when Lady Catherine (LaManna, also pulling off a dual role), arrives on the scene. Stanton’s dragon aunt is up in arms that her nephew is engaged to Elinor when he’s already promised to one of her two daughters, whose names and identities she can’t even keep straight.

But all hell breaks loose when Elinor and her crew discover a chest of bondage toys and dominatrix accouterments during a particularly challenging moment in their journey. At this point, the show crosses a Rubicon — or should I say jumps the shark? The gag, frantic to get a rise, runs roughshod over character and story.

Some might appreciate the slide into burlesque more than I did, but I was drawn to the complexity of the show’s protagonist, who, in noble Jane Austen tradition, refuses to compromise her intelligence for the sake of men. In a bright, charismatic performance, McCalla’s Elinor brings to life the character’s brainy charm and self-possession. She is the radiant center of “Regency Girls.”

But don’t underestimate Alabado’s Dabney, the nimble-witted maid, who is too dazzlingly resourceful not to make her presence known. Facing class prejudice along with gender oppression, she points out just how unequal English society happens to be. Alabado’s stunning portrayal elevates Dabney from servant to second protagonist.

Together, all of the women rise above their circumstances. Rockwell’s Jane and Redmond’s Petunia, while conceived in more flamboyant comic terms, are granted their own moments of self-discovery. Jane comes to understand that marrying for money isn’t half as satisfying as marrying for love, while Petunia assumes control over her own sexuality, rejecting the idea that she was born to be a baby machine.

Isabelle McCalla and Nik Walker, center, as Elinor and Stanton with the cast of “Regency Girls.”

(Jim Cox)

“Regency Girls” is the only musical comedy I can think of that includes an abortionist as a key character. Madame Restell, who operates a clinic offering reproductive services for women, delivers “How Long (In 1810)?” a powerful anthem decrying “the holy war” the patriarchy is waging against female autonomy. She can’t believe this militant opposition is still happening in 1810, though she might as well be singing about 2025, so persistent are the parallels.

LaManna brings down the house in a number that spells out what’s at stake in the musical. Marriage might be the all-consuming obsession, but “Regency Girls” makes clear that self-determination is really what these adventurous young women are fighting for.

The production could use some fine-tuning before it heads to New York. The staging, moving from antique to comic kink, accommodates the rapidly shifting story. (Anna Louizos’ mobile scenic design and David I. Reynoso’s playful costumes conjure Regency refinement without being trapped by it.) But sometimes the cast seems a bit frazzled by the musical’s leaps from a more character-based comedy to all-out travesty.

The happy ending that begins “Regency Girls” is eventually earned, though the conventional romantic story lines are rewritten. Elinor and her posse deserve more fulfilling lives, and with the help of canny Madame Restell, they manage to make their dreams come true on their own terms.