Justin Vivian Bond is onstage in a shimmering dress (a Jonathan Anderson!), catching every light in the theater and really laying into Anthony Roth Costanzo.

“Butcher! Butcher!”

Bond isn’t accusing Costanzo of murder, or trying to guess his side gig. The goal of this particular detour in “Only an Octave Apart,” their musical thrill ride of a two-person show, is to put a little hair on the chest of Costanzo’s critically acclaimed countertenor (the highest range for a male singer). Masc it up a little (or a lot). Make it butch-er.

It only kind of works. Costanzo gamely lowers his voice like a bucket into the bottomless well of Neil Diamond’s chest-bearing “I Am … I Said,” drawing forth a surprisingly convincing baritone for a few strained, brow-furrowing bars. But it’s all a bit too much disbelief to suspend — and it doesn’t help that Costanzo’s dress is just as fabulous.

“I mean it was fun, I liked it and all,” Costanzo says with slight resignation, turning to Bond, “but I miss the singing high part. You can sing high … ”

“I sing high all the time,” Bond replies.

And so forth. You get the gist. Or one of them. “Only an Octave Apart” is a show of many, many gists.

On its face(s), “Octave” appears to be a hybrid of cabaret (via the decades-spanning career of Bond, a genderqueer pioneer of the form and half of the iconic duo Kiki & Herb) and opera (via the soaring countertenor and career of Costanzo, who in May will resume his breakthrough titular role in Philip Glass’s “Akhnaten” at the Metropolitan Opera).

But when I took in the show last September during its limited inaugural run at St. Ann’s Warehouse in Brooklyn, it quickly revealed itself as something even more complex.

Inspired by and adopting their title from a savvily silly performance that Carol Burnett and Beverly Sills gave at the Met in 1976, Bond and Costanzo also channel the easy mastery of their muses — a virtuosity of sensibility. In my year-ender a few weeks ago, I noted that “Octave” sent me “ping-ponging between uncontrollable giggles and mask-dampening blubbers.”

But the long-term effect is a lingering craving for more of its freewheeling design, more of its binary busting of high and low, comic and tragic, masculine and feminine. How many experiences worth having have we missed, strictly because we thought they belonged in different rooms?

When I Zoomed with Bond and Costanzo last week, I brought up some of the words I commonly observe trailing them like pigeons after someone’s lunch. “Subversive” is one — a word I sometimes suspect is deployed by writers grappling with how to talk about a work’s queerness. (“The word used to be ‘camp,’ ” offers Bond. “Now it’s ‘subversive.' ")

Another word you’ll hear a lot around the “Octave” project is “unlikely,” as though the high drama, absurd humor and emotional force of opera and cabaret were separated by some insurmountable distance. (A glance at any gay boomer’s CD rack may demonstrate the opposite.) If anything, much like Bond’s and Costanzo’s gowns sparkling off each other’s light, “Only an Octave Apart” offers a fleeting chance for the two forms to fully reflect each other.

“I don’t think of myself as intentionally setting out to be subversive,” says Bond, 58. “I feel like people will make their descriptors of me, and it’s just my job to exploit them to my own benefit.”

“The point of the show is not to subvert opera or subvert cabaret,” says Costanzo, 39. “It’s actually to prove that there is no bulwark of classical music, and there aren’t these differences. The only thing I would say that is subverted is expectations. Everybody has these expectations of not just opera, but [the show] equally subverts the expectations that [cabaret] can’t be as heightened or emotional as opera.”

In “Only an Octave Apart,” grand operatic gestures, such as “One Charming Night” from Purcell’s “The Fairy Queen,” rub shoulders with Liza Lehmann’s 1917 “There Are Fairies at the Bottom of Our Garden” (based on a ribald poem from the pages of Punch magazine by one Rose Fyleman). A wistfully skillful stroll through the babbling brook of Jobim’s “The Waters of March” trickles into the cruelly gentle dusk of Joseph Kosma’s 1945 “Autumn Leaves” — Costanzo and Bond carefully interweaving Jacques Prévert’s French and Johnny Mercer’s English lyrics. Somehow Bowie, Bizet, Sylvester and both Didos (the Purcell one and the Eminem one) all end up on the guest list to the same party.

Costanzo showcases his control and care with a crystalline reading of Lizst’s “Über Allen Gipfeln ist Ruh”; Bond stretches “I’m Forever Chasing Rainbows” into an appropriately luminous arc that lands in a golden-voiced take on Tom Waits’s “Rainbow Sleeves.”

The two ventriloquize each other (I can’t recall ever belly laughing at the “Habanera” from “Carmen”) and duet themselves (with Costanzo singing both Count and Suzanna in “Crudel, perché finora” from Mozart’s “The Marriage of Figaro”). Ultimately, “Octave” feels like a show about the multiplicity of the self, the multitudes we contain and the way we depend on art to make sense of them all. (A performance of “Me and My Shadow” near the show’s start seems to italicize this possibility.)

Meanwhile, the uncanny chemistry between Costanzo and Bond feels throughout like a corollary to the obvious attraction between those arts we tend to keep apart. This nonbinary-in-every-sense approach to music is an act of liberation all its own, inviting devotees of either form to lose their bearings for a bit. In his essay for the liner notes to the forthcoming “Only an Octave Apart” album, the poet Wayne Koestenbaum offers listeners a helpful guide for navigating the wilderness between comfort zones: “There is no such thing as a wrong tree.”

Bond and Costanzo’s original idea was to workshop repertoire over the course of several shows at Joe’s Pub in New York. But [insert pandemic here] the idea flipped: Rather than a show that might lead to an album, the two recorded an album that could be realized into a show.

Produced by Thomas Bartlett (who was music director for the St. Ann’s performances, along with the show’s director and co-creator, Zack Winokur), the album is an arresting account of much of the material that preserves a good amount of the show’s spontaneous spark. The album will be released Jan. 28, and from Jan. 27 to 29, Costanzo and Bond will perform selections with the New York Philharmonic, featuring orchestral arrangements by Nico Muhly, as part of Costanzo’s “Authentic Selves: The Beauty Within,” a festival of music based on themes of identity. (Costanzo will also make a D.C. appearance on March 20 for a recital with the Shanghai Quartet at the Phillips Collection.)

For lovers of vocal music alone, the album earns its seat at brunch: The silken blade of Costanzo’s instrument and the soft gravel of Bond’s era-crossing croon create something of an irresistible textural combination. The collection also makes for an adequate holdover until the two figure out a future for the “Only an Octave Apart” show, which seems far more crucial now than when the two were just chasing rainbows.

“What’s clear to us as performers who do a lot of things is that we can’t let this go now,” says Costanzo. “This feels like the beginning of something. It was, for me, the best experience of my life, artistically.”

“I’m always happier at the end of a show than when I wake up in the morning, obviously,” says Bond. “But there’s something chemically transformational about doing a show. Acknowledging the world that we live in and running it through a prism to bring all the colors out of it.”

Anthony Roth Costanzo and Justin Vivian Bond perform with the New York Philharmonic Jan. 27 to 29. For tickets and more information, visit nyphil.org.