Sundance: In a quest to explore the vanity of the rock star's plight, the singer-songwriters have made a zany, unpredictable whatsit that turns it on itself.

Some 40 years after “This is Spinal Tap,” the prospect of another mockumentary on self-involved rock stars might not sound so appealing. Fortunately, “The Nowhere Inn” goes beyond the call of duty with a mesmerizing seriocomic descent into the madness of modern fame. This unclassifiable whatsit from singer-songwriter St. Vincent and BFF Carrie Brownstein works overtime to reinvent itself every step of the way, in a hilarious (if sometimes baffling) means of illustrating its outré point.

On its surface, “The Nowhere Inn” centers on St. Vincent’s road trip as she struggles to reconcile her onstage persona with her more grounded identity as Annie Clark. It’s a journey that’s absurd and eerie, ridiculous and deep. Pitched somewhere between traditional rockumentary tropes and a heap of zany Adult Swim shorts, it dips into the deadpan folksy satire of Brownstein’s “Portlandia” before veering into a shapeshifting psychological thriller worthy of vintage De Palma. Fans of St. Vincent’s vivid rock compositions won’t find much new information about her persona, but the movie provides a welcome extension of her artistry nonetheless.

While “The Nowhere Inn” marks the directorial debut of Bill Benz (whose previous credits include “Portlandia” and — surprise surprise — several specials for Adult Swim), it’s clearly co-writers Clark and Brownstein’s brainchild, no matter how little of it stems from real life. The movie’s opening chapter sets expectations for a project gone wrong, then delves into the deep bond between the pair (and former couple), as Brownstein sets out to make a movie about her pal on the road.

By this point, an opening prologue has already established expectations of something weirder afoot: Clark cruising through the desert in a limo, reading Maggie Nelson’s collection of cultural writings “The Art of Cruelty,” and contending with a driver who has never heard of her. “I’m not for everybody,” she sighs, before he abandons her in the dust, providing an all-too-convenient metaphor for…what, exactly? The alienation of the road? Clark’s frustrations over the bubble of luxury that protects her artistic identity while leaving her deeper self exposed to the elements? “The Nowhere Inn” leaves all that open-ended, while planting seeds for the stranger circumstances to come.

Within the confines of a traditional behind-the-scenes documentary, Brownstein is keen to capture the reality of Clark behind the intimidating shadow she casts onstage. As the first passage zips between St. Vincent’s explosive performances and the friends wandering through hotels and backstage crevices, Clark grows frustrated over the boring nature of her life. While “The Nowhere Inn” never quite feels like an authentic documentary, it hovers in that familiar mode long enough to let the traditional beats settle in, just in time for the filmmakers to disrupt them.

Brownstein, the Sleater-Kinney guitarist and “Portlandia” co-creator who always looks like she’s on the verge of winking to the camera, makes a convincing advocate for the impossible task of getting Clark to drop her performative instincts. (Losing faith in her ability to pull the project together, she googles “top 10 documentaries” in a desperate bid for direction.) “Let’s protect the fact that you’re normal,” Brownstein says, as the camera drifts to her subject’s reflection. Instead, St. Vincent heads the opposite direction, and the project goes with her.

When Clark decides to bring the seductive energy of St. Vincent into the project, “The Nowhere Inn” grows into a hazy assemblage of inspired strangeness, and the vignettes pile up so fast that Brownstein can’t keep up with them. All the while, the movie remains a wry meditation on St. Vincent’s real talent, with a handful of musical interludes both in tune with the zany plot and compelling on their own. But eventually they become part of the puzzle: As the project ventures deeper into an ambiguous space between the two writers’ intentions, it arrives as a beautiful, folksy rendition of “Year of the Tiger” performed alongside Clark’s made-up family, while her documentarian grows frustrated on the sidelines. Later, the movie arrives at a staggering sequence in which St. Vincent sings a haunting new title song behind the stage version of herself, confronting the source of authenticity at the root of her talent.

Or something like that. “The Nowhere Inn” plays fast and loose with its intentions, again reflecting the core of St. Vincent’s appeal (and sharing some DNA with Martin Scorsese’s quasi-fictionalized Bob Dylan documentary “Rolling Thunder Revue,” which bent the facts to capture its performer’s playful mystique). At the same time, Brownstein’s own conundrums sneak into the plot — her proud father insisting that she finish the project, her artistic desire at odds with the reluctant participant — as the movie has fun with the clichés of the vain, privileged creator from every direction.

At times a bit too enamored of these loose conceits, “The Nowhere Inn” sometimes registers as a cheap fuck-with-the-audience provocation that might have been better suited for a viral short (or several), but at its finest moments the movie conjures a singular vision steeped in zaniness, but not devoid of purpose.

It’s hard to pinpoint the exact moment when St. Vincent takes full control of “The Nowhere Inn,” but it’s somewhere around the moment she decides to roll around on a hotel bed in lingerie with her onscreen girlfriend, Dakota Johnson — forcing a mortified Brownstein to film the whole thing on an iPhone, while she begs for an intimacy coordinator — and a choreographed sequence in which she roams backstage with the camera just behind her shoulder, speeding toward a screaming crowd, while Brownstein begs her to get real. St. Vincent turns back, bathed in neon red, a guitar strapped to her shoulder and a look of contentment on her face. “I love you baby,” she says, “but I’m married to the road.” That’s the rock star ethos in a nutshell — and the essence of her plight.

It’s amusing enough to get lost in this labyrinthine plotting for a breezy 91 minutes, even if the twisty existential finale doesn’t quite justify the journey. Brownstein and Clark have thrown so much innovation into keeping the weird-for-weirdness sake rhythms moving along. Echoing “The Last Movie,” Dennis Hopper’s brilliant meditation on filmmaking hubris (if not matching its ambition), “The Nowhere Inn” finds reality bending in on itself, as the storyteller evades the pressure to adhere to the terms of the story mapped out for her.

“The audience doesn’t need me,” she sighs. “I’m just a vessel for their feelings.” Maybe, but “The Nowhere Inn” ultimately becomes a vessel for St. Vincent’s slippery persona that only adds to its intrigue. In the process of poking at the neurotic discomfort of revealing the person behind the art, Clark and Brownstein have crafted a shrewd celebration of exactly that.

Grade: B+

“The Nowhere Inn” premiered at the 2020 Sundance Film Festival in the Midnight section. It is currently seeking U.S. distribution.

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