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 familiar if spit-shiny New York City. The catch is that America has outlawed premarital sex, except for one night a year. It’s like “The Purge” but for sex.

Braun’s script was on the Black List, which rewards hooky, high-concept projects, often to mixed results. That is the case here. The film exists on the vapors of a bizarre plot and the appeal of hot actors. How does the government police premarital sex? With bio-sensors, of course. Singles receive tattoos that turn from red to green during the 12 hours that premarital sex is permitted. The why is less satisfactory—an upbeat news report cites lower teen pregnancy rates, a dated justification.

On the night of the Sex Purge, we find our winsome protagonists, Owen (Callum Turner) and Allie (Monica Barbaro). Both are despondent and desperate. A meet-cute turns into a meet-puke, and they spend one crazy night running into each other on increasingly urgent sex quests. Turner and Barbaro have charm up the wazoo, but repeated celebrity cameos distract from the nagging issues of the premise.

“One Night Only” doesn’t present fun escapism but a misguided, underbaked, and very straight-guy fantasy—essentially lots of people kissing in public. It’s tame and weirdly conservative. Not even their charisma can bolster the structural flaws. This film feels purged of a brain.