Sometimes a movie will turn softer than you thought it would — more sunny and upbeat and romantic, with a happier ending. Then there’s the kind of movie that turns darker than you expect, with an ominous undertow and an ending that kicks you in the shins. “Where the Crawdads Sing” is the rare movie that conforms to both those dynamics at once.

Adapted from Delia Owens’ debut novel, which has sold 12 million copies since it was published in 2018, the movie is about a young woman whose identity is mired in physical and spiritual harshness. Kya Clark (Daisy Edgar-Jones) has grown up all by herself in a shack on a marshy bayou outside Barkley Cove, N.C. When we meet her, it’s 1969 and she’s being put on trial for murder. A young man who Kya was involved with has fallen to his death from a six-story fire tower. Was foul play involved? If so, was Kya the culprit? The local law enforcers don’t seem too interested in evidence. They’ve targeted Kya, who is known by the locals as Marsh Girl. For most of her life, she has been a scary local legend — the scandalous wild child, the wolf girl, the uncivilized outsider. Now, perhaps, she’s become a scapegoat.

The film then flashes back to 1953, when Kya is about 10 (and played by the feisty Jojo Regina), and her life unfolds as the redneck version of a Dickensian nightmare, with a father (Garret Dillahunt) who’s a violent abuser, a mother (Ahna O’Reilly) who abandons her, and a brother who soon follows. Kya is left with Pa, who retains his cruel ways (when a letter arrives from her mother, he burns it right in front of her), though he eases up on the beatings. Barefoot and undernourished, she tries to go to school and lasts one day; the taunting of the other kids sends her packing. Pa himself soon ditches Kya, leaving the girl to raise herself in that marshland shack.

All very dark. Yet with these stark currents in place, “Where the Crawdads Sing” segues into episodes with Kya as a teenager and young woman, and for a while the film seems to turn into a kind of badlands YA reverie. Kya may have a past filled with torment, but on her own she’s free — to do what she likes, to find innovative ways to survive (she digs up mussels at dawn and sells them to the Black proprietors of a local general store, played by Michael Hyatt and Sterling Macer Jr., who become her caretakers in town), and to chart her own destiny.

You’d expect someone known as Marsh Girl to have a few rough edges. Remember Jodie Foster’s feral backwoods ragamuffin in “Nell”? (She, too, was from North Carolina.) Yet Kya, for a wild child, is pretty refined, with thick flowy hair parted in the middle, a wardrobe of billowy rustic dresses, and a way of speaking that makes her sound like she grew up as the daughter of a couple of English teachers. (Unlike just about everyone else in the movie, she lacks even a hint of a drawl.) She does watercolor drawings of the seashells in the marshland, and her gift for making art is singular. She’s like Huck Finn meets Pippi Longstocking by way of Alanis Morissette.

The English actor Daisy Edgar-Jones, who has mostly worked on television (“Normal People,” “War of the Worlds”), has a doleful, earnest-eyed sensuality reminiscent of the quality that Alana Haim brought to “Licorice Pizza.” She gives Kya a quiet surface but makes her wily and vibrantly poised — which isn’t necessarily wrong, but it cuts against (and maybe reveals) our own prejudices, putting the audience in the position of thinking that someone known as Marsh Girl might not come off as quite this self-possessed. Kya meets a local boy, Tate Walker (Taylor John Smith), who has the look of a preppie dreamboat and teaches her, out of the goodness of his heart, to read and write. It looks like the two are falling in love, at least until it’s time for him to go off to college in Raleigh. Despite his protestations of devotion, Kya knows that he’s not coming back.

You could say that “Where the Crawdads Sing” starts out stormy and threatening, then turns romantic and effusive, then turns foreboding again. Yet that wouldn’t express the way the film’s light and dark tones work together. The movie, written by Lucy Alibar (“Beasts of the Southern Wild”) and directed by Olivia Newman with a confidence and visual vivacity that carry you along (the lusciously crisp cinematography is by Polly Morgan), turns out to be a myth of resilience. It’s Kya’s story, and in her furtive way she keeps undermining the audience’s perceptions about her.

The scenes of Kya’s murder trial are fascinating, because they’re not staged with the usual courtroom-movie cleverness. Kya is defended by Tim Milton (David Strathairn), who knew her as a girl and has come out of retirement to see justice done. In his linen suits, with his Southern-gentleman logic, he demolishes one witness after another, but mostly because there isn’t much of a case against Kya. The fellow she’s accused of killing, Chase Andrews (Harris Dickinson), is the one she took up with after Tate abandoned her, and he’s a sketchier shade of preppie player, with a brusque manner that is less than trustworthy. He keeps her separate from his classy friends in town (at one point we learn why), and his scoundrel tendencies just mount from there. Did she have a motive for foul play?

“Where the Crawdads Sing” is at once a mystery, a romance, a back-to-nature reverie full of gnarled trees and hanging moss, and a parable of women’s power and independence in a world crushed under by masculine will. The movie has a lot of elements that will remind you of other films, like “The Man in the Moon,” the 1991 drama starring Reese Witherspoon (who is one of the producers here). But they combine in an original way. The ending is a genuine jaw-dropper, and while I wouldn’t go near revealing it, I’ll just say that this is a movie about fighting back against male intransigence that has the courage of its outsider spirit.