Review: â€˜Babyteeth,’ starring Eliza Scanlen as a teenager diagnosed with cancer, cuts deep

“Babyteeth,� a drama of unruly intelligence and churning emotional force, brings a jolt of unpredictability to a type of movie usually known for its grim, maudlin excess: the coming-of-age, coming-of-death story. Eliza Scanlen plays Milla Finlay, a 15-year-old who’s been diagnosed with cancer, and Essie Davis and Ben Mendelsohn are her parents, who respond to their daughter’s steady decline with varying degrees of panic, rage and resignation. There is no fault in these terrific stars, or in Toby Wallace’s arresting performance as the 23-year-old drug addict who crashes into Milla’s life, upending moments that might be her last.

The crash is quite literal. Milla is waiting for a train, closing her eyes and perhaps contemplating a leap onto the tracks, when Moses (Wallace), a flailing raw nerve on long, skinny legs, sideswipes her on the platform. He apologizes and tries to staunch her nosebleed, then asks if she has any money. Moses has a rat-tail, strung-out eyes and a tattoo on his cheek that might as well read “bad news�; Milla, instantly smitten, brings him home to dinner. Her mother, Anna (Davis), and father, Henry (Mendelsohn), look on with a kind of dumbfounded helplessness: If this creep really is the fulfillment of their smart, sensitive daughter’s dying wish, who are they to argue?

That’s the general outline of the story, directed by Australian filmmaker Shannon Murphy and adapted by Rita Kalnejais from her own play. Some of the material’s stage origins are evident in the screenplay’s barbed confrontations, its carefully modulated verbal tension and the confinement of much of the drama to the Finlays’ comfortable suburban home. (The film was shot in Sydney.) But Murphy, making a strong feature debut (you can see her work on the third season of “Killing Eve�), grasps that the difference between the theatrical and the cinematic is blurrier than we might think, and that the brand of psychological drama she’s pursuing has rich antecedents in both traditions. With a restless camera that bobs and weaves from one scene to the next (the director of photography is Andrew Commis), she scrambles the narrative along with our expectations, seeking a formal syntax that will mirror Milla’s volatile state and that of her deeply shaken family.

That syntax proves elusive at first. The nearly two-hour film is somewhat archly divided into a series of vignettes, most of them bearing glib, sardonic chapter titles. Individual moments sometimes veer unsteadily between comedy and pathos, rather than achieving a seamless amalgam of both. My own concern while watching “Babyteeth� was not that it might behave too much like a play but rather that it might fall into an overly familiar variant of suburban movie misery, well known in the U.S. (“American Beauty,� anyone?) but capable of flourishing anywhere in the world with drugs, psychobabble, backyard swimming pools, alluring neighbors and other distractions favored by the dysfunctional bourgeoisie.

The movie fortunately escapes this trap, largely by allowing its characters to escape whatever convenient labels we might attach to them. This proves especially crucial with Anna and Henry, whose anxiety over Milla’s health exposes and deepens the cracks in their marriage; they have a lot of history, and a lot to judge. Anna, once a promising musician, now spends most of her time agonizing over Milla. Henry, a psychiatrist, retreats into his own distractions and avoids confrontation at every turn; he attempts similar preemptive tactics with his wife, prescribing heavy medication to temper her bouts of depression and anxiety.

Mendelsohn and Davis, among the finest Australian actors working today, are both awfully good at villainy, which is why their characters’ emotional restraint and fundamental decency here feels refreshing as well as true. You could almost warm your hands over the smile that occasionally creeps onto Anna’s face, as when she enters a room to the delightful sight of Milla dancing up a storm, blithely unconcerned with whoever might be watching. That particular scene seems emblematic of “Babyteeth� as a whole: As she approaches what could be a cruelly short-lived womanhood, Milla’s increasing recklessness feels like a defiant eruption of life force. Her decisions and desires are a mystery that her parents and the audience are left trying to solve.

The wigs that Milla wears throughout the movie — one long and blond, one short and turquoise — are a plot device, initiated by her intensifying rounds of chemotherapy, but they also serve as a barometer of her rapidly shifting moods. The dynamic soundtrack, intermittently hijacked by Anna’s piano and Milla’s violin, offers clues of its own. Some of the best, briefest scenes explore Milla’s growing sense of isolation at the school she attends from time to time, and where she often confronts the casual thoughtlessness of classmates and friends.

She’s always a person and never a flow chart. Her acts of rebellion — brazenly flirting with Moses, running away from home for a night on the town — exist alongside scenes of warm, wordless affection with her parents. Their devotion to her is never in doubt, even when it’s tested by her wildly inappropriate taste in boyfriends. Moses is an overgrown lost boy, devoid of any ambitions beyond his next fix, and one of the movie’s best qualities is how — without softening his rough edges or pleading for our sympathy — it gets us to see what Milla sees in him. Which becomes, in turn, a way of seeing Milla herself more clearly.

You might have seen Scanlen recently in the HBO series “Sharp Objects� and in Greta Gerwig’s “Little Women,� in which she played characters who also struggled with long-term illness. Those afflictions may superficially unite them, but thanks to Scanlen’s mercurial screen presence, you are likely to come away marveling at their distinctions. When “Babyteeth� gazes away from her for too long — as when it tries to accommodate side characters like Milla’s expat music teacher (Eugene Gilfedder) or a neighbor (Emily Barclay) who strikes up a friendship with Henry — its focus tends to falter.

Milla re-centers its gaze beautifully; the movie seems to find its confidence and purpose at roughly the same time she does. It’s telling that in one of her final gestures — by which I mean only that it takes place near the end of the story (no spoilers) — she gently pries a camera out of someone’s grasp, as though she were taking ownership of something. It’s a simple, insistent act that, like so much else in this sneakily moving film, reverberates with love.