"Promising" is indeed the word for Emerald Fennell in the wake of her startling debut feature as a writer-director with Promising Young Woman.

Initially, Promising doesn’t seem to promise all that much. First glimpsed in a dissolute state in a nightclub, Cassie (Carey Mulligan) cuts the pathetic figure of a hopeless drunk. She looks a mess and seems not to care, barely doing the minimum at her coffee-shop day job. For her 30th birthday, her parents give her a suitcase. Time to move out, young lady.

Not yet entirely adept at handling exposition in a seamless, unobvious way, Fennell informs us that Cassie attended med school but dropped out. In due course, she runs into a former classmate, Ryan, who’s now a pediatric surgeon. This optimistically turns into an all-day date, but another blast from the past in the form of another guy sets off some different memories.

Up to this point, the pic seems a bit hackneyed, a look at a woman who’s still behaving like a dumb, substance-abusing, club-going kid when she hits the big 3-0. But almost as if announcing a shifting of gears into something far more significant, the director begins announcing chapter heads with bold Roman numerals – we know something more is up.

Chapter I involves Cassie’s encounter with Madison, a former friend and classmate now married to a wealthy guy who, it seems, might have had something to do with why Cassie dropped out of med school. Matters become more sinister in Chapter II when Cassie returns to her old school for a confrontation with the dean, who occasioned the girl’s departure from academia. Chapter III begins with Cassie appearing at the door of another academic, who had made threats against her unless she dropped her case. There is subsequent talk of an out-of-control bachelor party, a notorious videotape and other sordid doings, all in the nature of things that used to be hushed up and never spoken of again but are now being brought out into the open.

It only gets worse – far worse – in Chapter IV, with Fennell going to astonishing lengths both in detailing the damage done to Cassie, the efforts made to cover up and the long reach of much-delayed retribution. Promising Young Woman is a film that dares to take a chance, and wins.