A cringe-inducing sight greets us at the beginning of Promising Young Woman, the feature debut by Emerald Fennell. In a crowded nightclub, the gyrating bodies before us are all of a certain type: schlubby, sweaty guys, all wearing variations on the chino-and-button-down uniform of the modern office. As we soon learn, the movie is interested in scoping out the latent predators hiding in this unassuming display. What looks pathetic on the outside conceals the threat of real damage - something the lead character knows all too well.

Promising Young Woman introduces us to Cassie (Carey Mulligan) while she’s in the middle of her latest mission to root out these toxic guys before they can hurt someone. Pretending to be nearly blackout drunk, she encourages a nearby “nice guy” (Adam Brody) to call her a ride, and doesn’t protest when he redirects the car to his own apartment. She allows him to cop a feel, but suddenly drops the act, frightening the daylights out of a guy who was all too ready, moments before, to abuse his power over her. The next thing we know, Cassie is tallying another mark in a notebook, indicating she’s been waging this war for a while, and intends to keep doing it.

The villains of the movie are not the simplistic, leap-from-the-bushes variety of predator. Many don’t even have names. They are the men who put on a friendly face, who convince themselves and their victims that they mean no harm, that everything is consensual, and that anyone who complains afterwards was “asking for it”. They take advantage, wittingly or not, of unwritten social rules that allow them to fade into the background when threatened, escaping to ruin someone else’s life some day.

Fennell thus sweeps us along into a film that follows many of the beats of a traditional revenge film, but none of the violence. As cathartic as it may be to want Cassie’s enemies to get served more painful justice than they do, it’s clear that Fennell (who also wrote the screenplay) doesn’t want to tip her heroine into the kind of villainy she’s supposed to be fighting against. Cassie may be filled with rage, but something is keeping her from going full Lorena Bobbitt.

It doesn’t stop Cassie from going about her crusade in the most stylish way possible. If her background hadn’t been medical school, you’d think she double-majored in costume design and spycraft; all of her stings involve colourful outfits and obsessively researched plans. You begin to think she’s singlehandedly supporting her town’s industry of shady fixers. Setting aside the seriousness of her character’s objectives, Fennell still wants us to enjoy ourselves.

It’s Cassie’s time in medical school where all her problems began. Alienated by the popular kids in the program, Cassie’s best friend Nina was her lifeline, until a traumatic attack at a party took Nina away from her. Cassie drops out, starts working at a coffee shop, and is content to while away her time with her weekend predator-shaming, until she hears that the principal aggressor at the party (Chris Lowell) is back in town for his wedding. Cassie decides to upgrade her efforts, aiming to take down an entire network of abusers and their accomplices, even if she has to give up everything to do so.

Nevertheless, Mulligan’s performance makes it clear that Cassie isn’t some sort of singularly focused warrior. She wants a “normal” life as much as anyone, and is painfully aware of how her distrust of any man who crosses her path is hurting her. When Ryan (Bo Burnham), a former acquaintance from school, asks her on a date, Cassie desperately wants to connect with him, but it’s made almost impossible, given the fine line between normal dating and the poisoned encounters that Cassie usually seeks out.

It turns out that Cassie won’t be able to rest until she satisfies her higher calling. I won’t spoil how it turns out, but even though the film makes us expect fireworks, we get something more like a land mine. Cassie reasons that if society makes it too easy for abusers to squirm out of consequences, she’ll have to set a tighter trap. The structure of Fennell’s movie echoes its character’s tactics: hook us with colourful, tempting packaging, but deliver a subtler message once we’ve taken the bait. If Fennell’s work is this good on her first try, I’m intensely curious to see what else she has in store.

Promising Young Woman gets three and a half stars out of four.

Stray thoughts

• Casting Burnham as the love interest was a great choice; he carefully incorporates some of the darkness from his stand-up work into his role here.

• The idea of Cassie as a Batwoman-like figure striking fear into the hearts of the nightlife has to be what appealed to Margot Robbie, one of the film’s producers.