In a basement studio under Chicago’s Oriental Theatre, things are getting dramatic — and a bit surreal. A 14-piece orchestra is swelling to a cinematic crescendo. Three actors — portraying a sponge, a starfish, and a squirrel — mime their struggle to reach the top of an underwater volcano. Just as the music reaches its peak, one of the actors, in a voice that sounds not unlike a certain invertebrate fry-cook, cries out, “Give me the eruptor interruptor!”

The musicians fall silent, waiting. …

“… Aaand then we don’t have this part yet,” says orchestrator Tom Kitt, who’s overseeing this rehearsal session for “The SpongeBob Musical.” He’ll finish the rest later. For now, it’s a cliffhanger.

“SpongeBob” is also a cliffhanger for Broadway rivals. The big-budget production — costing between $15 million and $20 million — which opens in Chicago to critics June 19 with New York in its sights, arrives under the auspices of a deep-pocketed entertainment conglomerate, and touts a powerhouse international brand that stands poised to absorb a major share of Broadway’s ultra-profitable family business.

But these are dangerous waters. Nickelodeon, the Viacom label that originated and oversees the “SpongeBob SquarePants” property, is a Broadway amateur, embarking on a stage adaptation that, if it doesn’t strike exactly the right balance, risks alienating fervent multigenerational fans. The storyline is entirely new — it’s not based on an episode of the series or on one of the two “SpongeBob” films — and its score comes from a disparate group of artists, including John Legend, T.I., Panic! at the Disco, and the late David Bowie.

Fans, not to mention the ticket-buying public at large, may be predisposed to skepticism. Because at first blush, it’s almost impossible to get your head around what the offbeat undersea realm of Bikini Bottom could possibly look like onstage.

“We are talking about a wholly original musical, based on something that’s entirely two-dimensional, with a score that’s by a diverse group of musicians, and a group of theater creators who are maybe not the most commercial,” admits executive producer Susan Vargo. “There are a lot of moving pieces.”

Leading the creative charge is director Tina Landau. As a Steppenwolf member best known for serious Off Broadway fodder like “Head of Passes” and “Floyd Collins,” she’s not the most obvious choice for a splashy musical based on a cartoon. But she won over Vargo and Nickelodeon with a human-powered, found-object vision that aims to match the animated series’ indie vibe without striving for a literal translation. No foam heads required.

The physical production is big and colorful, but steers clear of massive technological demands. The sets and costumes (by “Fun Home” designer David Zinn) all have a homemade, low-tech vibe.

“I’ve been leaning into this kind of antic, unexpected, surreal, edgy sense of humor and sense of Bikini Bottom,” says Landau. “It’s accessible to children, but there’s something a little trippy and psychedelic and topsy-turvy about this world. I just loved the idea of creating a universe
from scratch.”

It’s been eight long years of development for Landau and Nickelodeon, which was intrigued enough by the possibilities of a cross-demographic stage musical to fund the ongoing work, but wary enough to need to be convinced that it would be, in Vargo’s words, “surprising, inventive, and exciting to a ‘SpongeBob’ fan of any age.”

According to Cyma Zarghami, the head of Nickelodeon: “There was never a financial imperative. But as a franchise manager, you have to continuously think about ways to reinvent.” The discovery that one quarter of “SpongeBob” watchers are adults without children encouraged Nick to believe that the property might be a good fit for the multigenerational Broadway audience.

Landau’s audition for the network began with a series of collages focused on casting or design or the mood of the show, progressed into an initial movement and physical comedy session (during which they discovered their 24-year-old SpongeBob actor, Ethan Slater), and then moved into the development of the script and score by adding book writer Kyle Jarrow (“A Very Merry Unauthorized Children’s Scientology Pageant”) to the team.

Landau and Jarrow pitched a handful of potential narrative choices to Nickelodeon, which settled on the one with the highest possible stakes: the end of the world. In “The SpongeBob Musical,” an underwater volcano threatens to destroy Bikini Bottom, sending the town’s residents into a panic — and SpongeBob on a quest to avert disaster.

For Jarrow, the work lay in discovering two hours worth of high stakes in a world that mostly exists in 11-minute snippets. “What felt like the hardest thing for me,” he says, “was figuring out, for each of these characters, what’s an emotional arc that feels true to who they are, but also feels like we get to see them change over the course of an evening.”

It was Landau, inspired by the varied soundtrack to the 2004 “SpongeBob SquarePants Movie,” who came up with the idea of asking different musicians to each contribute a song to the score. She and Jarrow plotted out precise story beats where tunes should go, and which artists might match each mood. The diversity of the music, she reasoned, would gel with the animated series’ non-sequitur spirit.

Nickelodeon’s executive in charge of music, Doug Cohn, helped connect the show’s collaborators to the artists on their musical wish list. The result could make for an orchestrator’s nightmare, but Kitt (“Next to Normal,” “If/Then”) counters that his job is to preserve each artist’s unique sound, not sand off the edges. “T.I. wrote a great song; I want it to sound like T.I.,” he says. “Aerosmith — Steve Tyler and Joe Perry — I want it to feel like a song they would be in the studio making.”

In that basement studio at the Oriental, it’s certainly true that Bowie’s tune sounds like it could have been written by no one else, even when performed by a cast of actors and an orchestra. The song, lifted from the 1995 album “Outside” and given new lyrics (by Jonathan Coulton) with Bowie’s blessing before he died, is called “No Control.” It’s full of broody anxiety over the eruption that threatens Bikini Bottom — but it also serves as a reminder of the variables over which Team SpongeBob has no control, ranging from critical response, to which theater owner will commit a Broadway house to the project, to exactly when the musical will debut in New York.

Can SpongeBob save the day in Chicago and on Broadway? Stay tuned.