The friendship between young Frances (Chloë Grace Moretz) and Greta (Isabelle Huppert) starts off sweet, before it turns sinister. Focus Features

Imagine you’re a 20-something living in New York City and you spot a particularly nice and structured green leather handbag on the subway. Do you report it to the MTA? Ignore it and move on? Claim it and its contents for yourself? Return to the owner?

For Chloe Grace Moretz’s Frances, a wide-eyed transplant to the big city, it’s obvious: You go alone to hand-deliver the bag to Greta Hideg (Isabelle Huppert), who, according to the identification card you find, is a tiny, nice-looking woman in her 60s.

This is the first of many mistakes Frances makes in writer and director Neil Jordan’s (“The Crying Game,” “Michael Collins”) stylish and knowingly over-the-top “Greta ,” a dark, Brian De Palma-esque fairy tale about the dangers of trusting a lonely soul. She might just turn out to be a wolf, right?

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The film starts out like a rom-com, introducing sweet Frances working in a fancy Manhattan restaurant and riding the train alone back to the spacious apartment she shares with her roommate Erica (Maika Monroe), a wealthy party girl with more street savvy than dear Frances has. Erica suggests they take the cash in the purse and use it for colonics. But Frances, who recently lost her own mother, wants to do what she considers the right thing, and before you know it, she and Greta are fast friends and it’s nice for a while! They take walks in the city, have long talks about life over homemade meals and red wine, and even adopt a dog for Greta. It’s only when Frances stumbles on something that frightens her enough to ghost Greta that things get bad.

Greta, a widow and mother to an estranged daughter, lives in one of those impossible old city houses that’s been so built up around, it’s almost hidden now. Inside is a cozy, but decaying mishmash of elegant vintage wares – threadbare rugs, torn upholstery and black-and-white photos in dusty silver frames that looks like it belongs to a 95-year-old, not a 65-year old. (My first thought was, “Is this Greta’s mother’s home?”)

It’s a not so subtle metaphor for the societal invisibility of the aging woman and a theme of this otherwise berserk but enjoyable film that I’m having trouble reconciling. First, because Huppert isn’t nearly as old as the film seems to want her to be, and second because perhaps narratives further alienating older people by casting them as creepy and crazy outsiders are kind of evil. Is it because it’s written by men (Ray Wright and Jordan are co-credited as the screenwriters)? It’s possible considering how ridiculous and underdeveloped a character like Erica is.

But Huppert seems to be enjoying herself fully leaning into Greta’s insanity, so perhaps this one can get a pass. She helps elevate the film from its self-consciously B-movie roots to be something that’s actually pretty good. Her descent into madness is truly delightful to watch, and she’s very good at making you think that maybe Frances really is overreacting. What threat could a 65-year-old classical music-loving waif in gloves and tweed really pose when she’s ordering a kir royale at a nice restaurant?

Moretz is solid as Frances, and it’s honestly nice to see her play someone earnest for once. She seems to have gotten into a little bit of a typecasting rut as jaded mean girls, and this is a pleasant and promising departure from that.

Don’t go into this expecting some feminist treatise though. “Greta” is about as retrograde as you can get, but accepting that, it’s also tremendously silly and kind of a blast.

‘Greta’

Rated R for some violence and disturbing images.

Time: 1:38.