In an alternate fascist present in “One Night Only,” premarital sex is outlawed except for one precious 12-hour stretch each year. Naturally, New York City and its eligible—and very pent-up—denizens go all out for the annual occasion, expressing their long-awaited freedom through exuberant and often abbreviated partywear. “It has to be this New Year's Eve-type of theme,” says the film’s costume designer Jacqueline Demeterio, referring to her mood boards and discussions with director Will Gluck.

Pharmaceutical jingle singer Allie (Monica Barbaro) wears her hopes and expectations for this once-a-year occasion and potential liaison in a romantic, chocolate-brown lace slip dress by Reformation and Paris Texas high-heel mules. “You said, ‘tasteful and elegant!’” she exclaims to her roommate Jacinta (King Princess), clad in an illusion-panel, floral corset minidress by Fleur du Mal and thigh-high boots, while gesturing at her dress. “This is tea length!” As Jacinda immediately meets a match in the bathroom line, Allie daydreams of making an emotional connection with last year’s hook-up who then ghosted her.

“The lingerie-type slip-dress was her version of sexy, but it was still covering everything, with a proper length and neckline,” says Demeterio. “But she's looking for this more meaningful relationship for the night. So I feel like the dress reflected that, where it wasn't this plunging one that she ends up in …”

Because the unofficial dress code for the evening—as evidenced by the explosion of vibrant sequins and limb-baring minidresses across the city—is, as Allie's friend Arya (Quintessa Swindell) puts it, "a shiny object … something that screams 'down to clown.'" As Demeterio explains: “I wanted it to be a little flashy. This all takes place in one night—more or less—so everything that you see on the screen really has to tell that story and be very impactful of what this night actually is.” Demeterio, who looked to nightlife style and fashion editorials for inspiration, adds: “The background is its own whole story in itself of what is going on with all these couples behind closed doors—or not closed doors.”

A dejected Allie almost gives up on the festivities to play sad songs on her keyboard at home, until Arya convinces her to give it another shot—encouraged by an emerald-green, open-back, and ultra-mini dress left behind by an ex. “This is tiny! Are you sure this isn’t a top?!” Allie exclaims, stepping outside her literal and figurative comfort zone of classic “French girl” button-down shirts and Levi’s 507 jeans—also famously Carolyn Bessette Kennedy’s go-to denim. “It’s so outside of who she is, and I did want her dress to stand out,” says Demeterio, who transformed an Alex Perry dress—turning a cowl-neck into a sleek, low-plunge V and shortening the hemline. “Monica wanted the dress shorter and shorter, and I'm like, ‘Um, you're gonna be upside down! We need to tack you in. There was a lot of tape involved.”

Embarking on her second attempt—of several—to find a legally sanctioned hook-up, Allie immediately bumps into pizzeria owner Owen (Callum Turner). The encounter kicks off an evening of near-misses, tension-filled banter, and physical comedy—including fishing a precious condom out of a sidewalk drain, headfirst. “This dress is so important. It had to tell a lot of different stories,” says Demeterio. “Throughout the night, she starts to get more comfortable with herself in this dress and comes into her own self. I felt like the dress wasn't wearing her anymore.”

The night doesn’t begin as Owen expected either. Over a carefully orchestrated omakase dinner, his girlfriend Malika (Maya Hawke)—channeling “upper echelon” untouchability in a champagne silk shift-dress, dotted with delicate sequin embroidery, by Miu Miu—announces that she’s redeeming her one-night pass with someone else. She needs to “explore,” she says, and “You are super programmed,” she tells Owen, who, of course, organized his outfit for the big evening: a grey knit polo shirt by Purdey, black Bottega Veneta pants, an APC zip-up bomber jacket, and distressed Dr. Martens boots. “His outfit was also tricky,” says Demeterio, about designing another character-driven look to take Owen through a night of mishaps and adventures. “He's cool, but a little nerdy. We just tried classic menswear things on him. Is it too trendy? Is it too cool? Callum loves a polo himself, too.”

Deciding to crash a VIP party together—but not together-together—Allie calls out Owen and his polo for being underdressed. His indignant response: “This is Buck Mason!” “It wasn’t, but we did have a Buck Mason for him,” says Demeterio. She honored the script by draping a brown plaid jacket over Owen’s shoulder—and a Claremont Pizza-branded Tom Ford crewneck t-shirt—as he heads from his pizza shop to the barber and florist, preparing for his big night with Malika. 

During the night, a sheepish Owen has another unplanned meet-cute with Allie in borrowed clothes: an NYPD jacket and basketball shorts presumably fished from the lost-and-found. “It was just to make sure that this looks ill-fitting or you see his legs,” says Demeterio. “He was such a mess at that point. But he is a trooper, Callum.” 

Because neither Owen nor Allie could have dressed for the unplanned events of the evening—which, spoiler, work out well for both of them in the most unexpected ways. “It’s this night filled with shenanigans and just this craziness,” says Demeterio.