Tina works security at a Swedish port. As passengers walk up a long corridor toward the terminal, she stands and looks at them. And she sniffs. Sometimes her lip curls, revealing stubby, yellow teeth. Her jutting brow ridge furrows a bit. If something agitates her, she growls. Quietly, as if trying to suppress it.

She’s good at her job. For some reason she can literally sniff out guilt. Usually she catches banal lawbreakers — underage kids trying to smuggle a little booze. But one day she detains a well-dressed man who has a SIM card full of child pornography.

Tina, the main character in Ali Abbasi’s “Border,” lives removed from society, in a forest house she shares with a manwho raises dogs that she can’t be around. Enlisted by higher authorities to dig deeper into the child pornography case, she’s suddenly around people who are curious about who she is and what she can do. She’s not entirely sure about these things either.

Enter Vore, who has facial features and a physical bearing similar to Tina’s. Vore studies insect larvae and collects maggots. (Not just for the sake of collecting them, either, as we’ll soon learn.)

When Vore comes off a boat and looks Tina over, Vore grunts too, in a manner like Tina’s and makes a face that toggles between a leer and a sarcastic sneer. Tina (Eva Melander) doesn’t know what to make of Vore (Eero Milonoff). But Vore has a thorough understanding of the secrets that Vore and Tina share. Secrets that Tina’s father, who’s struggling with dementia, has withheld from her for years.

I don’t know a lot about Swedish folklore, so I was in an especially cold state as I went into this movie, written by Abbasi, Isabella Eklof and John Ajvide Lindqvist (also the writer of the 2008 film “Let the Right One In”), from Lindqvist’s short story. As cold as possible is a good way to see it. This is a movie that aims to startle in overt and subtextual ways; the less known before viewing, the better.

IN ITS first sequences, “Border” is shot and edited in a straightforward style that suggests a documentary. The makeup work, by a large crew, alters the appearance of Melander and Milonoff most credibly. The actors are stalwart in depicting the unusual behavior of their characters. A scene in which Vore tries to convince Tina that the maggots that seem to be the biggest part of Vore’s diet are indeed scrumptious is one of the most delightfully squirm-inducing moments here.

As the movie continues, it splits its narrative. One thread follows Tina as she helps the authorities catch the child pornographers. Another shows Vore and Tina enthusiastically and sexually explicitly exploring their affinities. And here “Border,” which won the top prize in Cannes’ “Un Certain Regard” slate this year, becomes a somewhat more conventional genre film.

Indeed, the final plot twist will elicit a nod from anyone conversant with 1980s Hollywood thrillers. But by this point, the movie has served up so many surprises, jumpy moments, and occasional but well-earned laughs that the familiarity is acceptable.

“BORDER”

*** 1/2

(R, 1:50; in Swedish, with subtitles)

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