From the opening flute, rising from a moan to a shriek over the clack of wood blocks, Michael John LaChiusa’s See What I Wanna See announces its debt to antique Asian inspirations. That the truth-is-elusive parable Rashomon looms large among them will surprise no one who’s looked twice at the title—or once at the program, where the caption “R Shomon” sits atop the first-act song list.

What’s more eye-opening is what happens after intermission—how far removed LaChiusa’s second act is from his first and what different sorts of truth it seeks.

A quick summary: After a dark little prelude involving a set of samurai-era lovers and their unhappy end (hat tip to “Kesa and Morito,” a fatal-attraction story by “Rashomon” author Ryunosuke Akutagawa), the action moves to 1951 New York, where a movie-theater janitor (Bobby Smith) sits on a chair in a cone of light, telling an unseen police detective about the rape and murder he’s either witnessed, stumbled upon, or participated in.

A beat, a light change, and a thief (Matt Pearson) steps downstage center to describe his part in the crimes in question—cue the knowing chuckles from the Kurosawa fans—and we’re off to the races, with flashbacks within flashbacks and at least four conflicting accounts of how the death went down. (Rachel Zampelli is the lounge-singer Wife, either a lady or a tramp, whose shiny-suited Husband, played by Tom Zemon, ends up with her stiletto in his chest.) And with LaChiusa offering no more answers than his source material does, the first act ends on a note of worldly ambiguity that’ll be catnip to the cynical, even as it leaves less jaded types mourning the thinness of the characterizations and wondering about the point.

After intermission, after another dalliance with Morito and Kesa—the same dalliance, actually, only with the narrator’s perspective reversed—the same players take on new personas in contemporary Manhattan, with Smith once again setting things in motion as a priest who’s lost his faith in the wake of a city-shattering tragedy. A prank he stages to mock New York’s remaining believers—he posts flyers promising a miracle, time and place specified—takes on a life of its own, snowballing until it ensnares even the skeptical residents of a community where hope has been in short supply, and at the appointed hour a dramatic phenomenon does in fact manifest itself. If it’s not the one the priest has prophesied, it’s something nonetheless, and if it doesn’t change the world it certainly changes him.

Matthew Gardiner’s production, staged in the smaller of Signature Theatre’s two houses, can’t quite bring the night’s parts into balance, but that’s not necessarily the director’s failing. The show is a disjointed, hybrid thing, to start with: LaChiusa put together an early version of “R Shomon” as a stand-alone piece as far back as 1996, and the slick noir story of the first half certainly feels like the work of a less mature artist; it’s all surfaces and attitude, though handsomely conceived by Signature’s design team. The second half, “Gloryday,” was begun later; it didn’t acquire its post-apocalyptic, modern-day messianic groove until after the events of 9/11, of course, and the two playlets weren’t performed together until 2005, for the premiere of See What I Wanna See at the Williamstown Theatre Festival.

And in some ways the two halves actively fight each other: The comparative richness of the characters LaChiusa offers up in “Gloryday”—a drug- and sex-addicted actress, a burned-out CPA who’s chucked it all to live in Central Park, a sharp-tongued, knowing Italian matron—makes “R Shomon” seem even thinner (if no less stylish) in retrospect. The urbanity of Act 1, meanwhile—the clean structural games, the brutal snap, and the knowing sneer—holds up an unforgiving mirror to Act 2, which feels less lean and more sentimental by comparison.

The point, or one of them, is that sneers and cynicism have less currency in a world that’s been shaken to its core: We may not be any surer of the truths we’re groping after, but we’re presumably allowed to yearn for them a little more transparently without fear of being mocked. (It’s a point underscored by an 11th-hour change of heart for that Italian matron, the priest’s hard-nosed, unapologetically atheist Aunt Monica—whose name, that of the once-pagan St. Augustine’s mother, cannot be an accident coming from a dramatist born into an Italian Catholic family.)

And there are pleasures to compensate for the imbalances. The dialogue, particularly in Act 1 but substantially in Act 2, is admirably snappy; the songs that grow out of it so organically are angular, sophisticated, and every bit as smart as you’d expect from the creator of the Jazz Age orgy The Wild Party and the Van Gogh fantasia The Highest Yellow. The band sounds just fine, and the vaguely grove-like feel of Adam Koch’s setting pays smart homage to the stories’ inspirations.

Zampelli and Zemon each have strong moments, particularly once the action moves to the 21st century. Pearson brings a knife-edge sharpness and a dangerously sexy knowingness to his “R Shomon” thief, and an appealing, unmoored sense to the TV reporter he plays in “Gloryday,” while Smith demonstrates again that he’s one of Washington’s go-to character actors, a player with a seemingly endless bag of tics and tricks from which to build memorable eccentrics.

And then there’s the fierce and funny Channez McQuay, who’s riotous and odd as a medium in Act 1, and who nearly runs off with Act 2 entirely as Aunt Monica. Miss her turn in See What You Wanna See, and you’ll miss one of the better examples of scene-thievery that’s likely to come your way this year.