allie

Every now and then a rom-com comes along with an absolutely ludicrous premise that we just sort of accept because it creates the unique conditions for watching a pair of budding movie stars fall in love. This year’s entrant is “One Night Only,” written by Travis Braun, directed by Will Gluck and set in a pretty familiar if spit-shiny New York City. The catch is that America, for some reason, has outlawed premarital sex, with the exception of one night a year, when singles can get their freak on. It’s like “The Purge” but for sex, so the Sex Purge.

Braun’s script was on the Black List, a collection of the best unproduced screenplays in Hollywood, which tends to reward hooky, high-concept projects, often to mixed results. That is most definitely the case with “One Night Only,” a film that exists on the vapors of a bizarre plot and the appeal of hot actors.

You probably have a lot of questions, and “One Night Only” is only going to satisfy some of them. How does the government police the premarital sex? With bio-sensors, of course, as explained by a drunken tech bro (Nicholas Braun) in an exclusive lounge. Singles receive small tattoos that turn from red to green during the 12 hours that premarital sex is permitted, body modifications that measure things like oxytocin and dopamine and whether one sensor is in close proximity to another. Sexual acts that are solo, distanced or parallel are permitted, yet many questions still remain about the kinds of hookups that can be had during the mandated ban.

The why of it all is much less satisfactory. An upbeat news report explains that rates of teen pregnancy are down, which is a very 1980s justification. The whole gambit feels dated and underexplored, both conceptually and politically — so you’re saying single straight people are an oppressed sexual minority? Maybe that idea should have been unpacked a little bit more.

On the night of the Sex Purge, the streets are flooded with attractive, thin, largely heterosexual couples making out all over the place. Perish the thought of being single and vulnerable, as they say on “Love Island,” on such a night, which is how we find our two winsome protagonists, Owen (Callum Turner) and Allie (“A Complete Unknown’s” Monica Barbaro). Owen’s a pizza maker whose girlfriend (Maya Hawke) wants to explore someone else; advertising jingle singer Allie has been ditched by her best friend (King Princess) for a prince.

These two strangers are both despondent and desperate. When they bump into each other on the street, a meet-cute turns into a meet-puke, and so the story follows an enemies-to-friends-to-lovers track, as they spend one crazy night continually running into each other on their increasingly urgent sex quest. The script does a good job of throwing up plausible obstacles and sticky situations for these two to navigate: price-gouged condoms, police raids, catfishing, injuries, parental ambushes, etc.

Turner and Barbaro have charm up the wazoo, and Gluck does a fair amount of key-jangling to distract from the nagging issues of the premise itself. There are repeated gags about Allie’s job singing covers of popular songs reworked for pharmaceutical companies and almost too many celebrity cameos. Every time a celeb’s face pops up it’s essentially an “ooh, shiny thing!” moment so that we stop thinking about the intricacies of the world where Sex Purge happens. Allie’s hopeless romanticism isn’t well-established, and there’s a whole complicated climax (no pun intended) involving the Empire State Building that could have been a lot smoother and more intuitive.

Allie’s most impressive feat is making it 12 hours in New York City in spike heels and a sequined micro-mini, but rom-coms are the stuff of fantasy anyway. Yet “One Night Only” doesn’t present us with fun escapism but, rather, a misguided, underbaked and very straight-guy fantasy of what something like this might look like, which is essentially … lots of people kissing in public? It’s tame and weirdly conservative.

Turner and Barbaro give it their best, but not even their charisma can reliably bolster the inherent structural flaws of this concept and its execution. “One Night Only” feels purged of a brain.

Katie Walsh is a Tribune News Service film critic.