The story is full of surprises, and an intriguing one is the basis for the world premiere of “Quamino’s Map” at the Chicago Opera Theater, which opened Saturday night at the Studebaker Theater in the Fine Arts Building.

It turns out that thousands of enslaved Americans fought alongside the British during the Revolutionary War with the promise of freedom and a pension across the Atlantic Ocean when hostilities ceased .

Belizean-born British composer Errollyn Wallen and American librettist Deborah Brevoort have taken this virtually unknown historical episode and followed it, creating a 90-minute opera loosely based on SI Martin’s “Incomparable World: A Novel.” Despite its compact runtime, it is a large-scale work with 29 singers in the cast and chorus and a 40-piece pit orchestra.

At its heart, “Quamino’s Map” is an ultimately impossible love story between Juba Freeman (tenor Curtis Bannister), a former slave who has just arrived in England, and Amelia Alumond (soprano Flora Hawk), a kind-hearted member of the Black from London. nobility.

But more broadly, the opera examines the notion of freedom, not just from physical slavery but also from societal and economic shackles, issues that all the main characters face in one way or another.

Nowhere is this truer than for Freeman, who travels to London thinking he’s escaped slavery only to discover a new set of chains: the Brits giving up on their promise of a pension and a law banning the work to black newcomers.

It’s a fresh and gripping story told in a smart and often captivating way. But at the same time, this story turns out to be a little too easy. That Freeman arrives in London, gets engaged to a wealthy woman, and is almost hanged for theft, seemingly within weeks, stretches the limits of credibility.

And it’s hard to accept the opera’s optimistic conclusion. Quamino Dolly (bass-baritone Damien Geter), a former slave and now mapmaker (a metaphorical feat) who becomes Freeman’s protector, encourages the newcomer to chart a new future by pursuing his love of the violin. He collects enough money to buy an instrument for the young man, but how does that help if the job is impossible?

Director Kimille Howard makes the most of this fast-paced story, maintaining a sense of continuity and pleasantly energizing ensemble scenes, especially those in London’s red light district.

Decors by designer Steven Kemp are simple but effective enough. The opera opens onto the London docks, which is suggested by brick building walls on either side with a sloping ramp between them and an enlarged historical map of London as a backdrop. With just a few additional sets and lighting changes, this arrangement adapts adequately to changing settings.

Wallen has written 22 operas, and it’s clear here that she knows what she’s doing in this engaging score, with its compelling melodic lines and lush, ever-varied orchestrations, all beautifully done by conductor Jeri Lynne Johnson. .

What’s most impressive is Wallen’s ability to change his style from stage to stage, from harpsichord and baroque effects for the high-society gatherings of the Alumonds to Broadway-tinged numbers for the stages. of red light, with jazzy riffs, hints of blues and harsh dissonances. along the way. The only thing missing is just a bit more emotional depth, which could have been provided by more traditional, full-bodied tunes instead of what often comes across as long recitatives.

The Chicago Opera Theater has assembled a strong cast, starting with Bannister, a focused, technically confident singer who possesses the stage presence to anchor this production and the acting chops to convey both Freeman’s joy and pathos.

More than standing up to him is Hawk, who lights up the role of Amelia with her strong, radiant soprano voice. One of the opera’s highlights is when she shows up late for an engagement party, and Wallen humorously recounts a feud between Amelia and her mother, Grace, and sister, Elizabeth (skillfully performed by the soprano Kimberly E. Jones and soprano Joelle Lamarre), with piquant exchanges of exaggerated baroque-style vocal ornamentation that requires impressive vocal dexterity to pull off.

Geter’s confident, resonant voice serves the role of Quamino well, but it’s odd that the character is described as an “old man” at one point, but no effort is made in terms of his looks or appearance. to suggest his age.

Other stars include mezzo-soprano Leah Dexter, who makes the most of her showy role as the whimsical dominatrix Mistress Paddington, and tenor Tyrone Chambers II. He animates the role of Dele Piebald, a mysterious beggar who is also a kind of seer who intervenes in this story.