Carey Mulligan is perhaps best known for portraying tragic ingénues, turning in memorable performances in roles like Ryan Gosling’s doe-eyed (and criminally underwritten) love interest in 2011’s “Drive,” and the evanescent Daisy Buchanan in 2013’s “The Great Gatsby.” In Emerald Fennell’s new “Promising Young Woman,” Mulligan finally gets the chance to subvert that persona in an Oscar-caliber reversal, dominating a film that delivers lacerating cultural commentary in exploitation-flick disguise. Given the marketing for this movie, you’d be forgiven for expecting a conventional rape-and-revenge plot-line, in the vein of “The Last House on the Left” or “I Spit On Your Grave,” but what actually shows up onscreen is something much more unexpected.

(Some spoilers in the discussion to come. You’ve been warned.)

Fennell’s film centers on the thirtysomething Cassie (Mulligan) a medical-school dropout who works in a Los Angeles coffee shop by day and frequents the local bars by night, pretending to be hopelessly drunk. Over and over, Cassie lures lecherous men into compromising situations before turning on them like a vengeful Artemis, forcing them to come face-to-face with their predatory behavior. Meanwhile, at the same time she struggles to form a relationship with her former classmate Ryan (Bo Burnham), a successful pediatrician who’s committed to persuading Cassie that maybe there are some good men out there after all.

It soon becomes clear, however, that this isn’t actually the story of Cassie’s own trauma, but rather that of her late classmate and friend Nina, who was cruelly assaulted while blacked out at a drunken party. For Cassie, perpetually haunted by the fact that she didn’t stop Nina from going to the fateful party in the first place, the only way to expiate her guilt is to make the perpetrators pay. Her key targets aren’t limited to the rapist and his accomplices: also on her list are the school officials and lawyers who swept the offense under the rug.

And it’s here that “Promising Young Woman” runs into a bit of a thematic snag. On the one hand, it’s clear that Fennell’s film is committed to a compelling defense of female agency: women should be free to go where they choose without the threat of being raped. In so arguing, the film amounts to a bruising indictment of anyone who would excuse sexual assault by saying well, she shouldn’t have been drinking in the first place. Responsibility lies with the perpetrator, not the victim. But at the same time, its protagonist is consumed with guilt for not undermining that agency—not stopping Nina from going to the party—and in framing her as a genuine heroine meting out justice against evil people, the movie suggests that this guilt is justified. If indeed individuals are solely responsible for their own choices, though, is Cassie genuinely inculpated by Nina’s exercise of her own agency?

The overall effect of this paradox is that it’s unclear how the viewer should feel about Cassie’s onscreen experience of guilt—and, by extension, her whole crusade. Does Cassie need to atone for her sins in this way? Is she or isn’t she to blame for what happened to Nina? Perhaps Fennell means the audience to simply sit with this unresolved tension—to leave it ambiguous whether “Promising Young Woman” is a tragic meditation on cycles of guilt and recrimination, or a triumphant account of an avenging, atoning angel bringing down swift retribution. But I think the latter is closer to the truth: in many ways, “Promising Young Woman” is the same sort of celebration of postmortem vengeance that made Netflix’s “13 Reasons Why” such a controversial hit.

That said, this whole issue is somewhat peripheral to the story’s intended direction. Far more memorable than its internal tension is the mood of pervasive threat that it conjures up, a mood rooted chiefly in its depiction of male silence—the willingness of too many men to make excuses for each other when forced to confront the impact of their actions on the women in their lives. And that, I think, is the film’s principal takeaway.

Technically speaking, “Promising Young Woman” is a standout, marked in particular by its arresting art design and cinematography. A pervasive 1950s aesthetic suffuses the film’s daytime scenes, which disappears entirely once the much grittier nighttime sequences begin—a nice visual evocation of the darkness that often lurks beneath the surface of everyday life. And to her great credit, Fennell avoids choppy editing in favor of lingering takes that her leads’ emotions to play out, lending real depth to her characters. Mulligan, as previously noted, is singularly great in the lead role—as is the supporting cast, notably Alison Brie, Christopher Mintz-Plasse, and Alfred Molina.

For those who might be put off by the subject matter, this is not an especially gruesome film—the real horror lies in the viewer’s imagination of what’s happening off-camera—but it is by no means an easy watch. It is, however, well worth your time. As an unsettling parable of deep wounds and delayed justice, “Promising Young Woman” is a tremendous success. (And I look forward to seeing whatever Fennell directs next.)