“Mah-mah.” That whispered refrain, delivered often throughout Mama by Lily (Isabelle Nelisse), is evidence of how thoroughly unsettling an innocuous phrase can become in the context of a film that knows how to wield it. Adapted from a short film by Andres Muschietti, who also directed, Mama is often an exercise in jarring suspense, lean in its approach to low-key horror and operating with an eye toward the humane. A parable for the morning-after pill generation, Mama is above all a film about a young woman’s efforts to accept motherhood, a status forced upon her with potentially life-threatening consequences. But unlike your standard Lifetime Original, the threat is literal.

When Lily and her older sister Victoria (Megan Charpentier) were one and three years old, respectively, they were taken into the woods by their father after the collapse of his double-dealing company led him to commit a grisly murder. Before he could commit two more, something in the cabin he found ensured that Lily and Victoria would always be safe from harm. Years later, their uncle Lucas’ (Nikolaj Coster-Waldau) exhaustive search finally pays off, when Lily and Victoria are found living in squalid conditions, crawling around on all fours like feral animals. Lucas appeals heavily to become the girls’ guardian, a choice more appealing to him than to Annabel (Jessica Chastain), a rocker chick who enjoys her bohemian lifestyle and has very little interest in inheriting two little girls as part of her relationship. The gender dynamics posed in the early scenes between Lucas and Annabel are fascinating by Hollywood standards; he the doting caretaker, she the increasingly distant lover who sticks around just because of the guilt of leaving him in such a delicate situation.

Mercifully, Mama wastes little time establishing that the presence from the cabin has followed the girls to their new home, and instead concentrates on what happens when, after an encounter between Lucas and that presence, Annabel is forced to look out for the girls. Chastain is more than up to the task of conveying Annabel’s slow evolution from borderline negligence to genuine affection, and contributes to Mama a nuance that the film might not have enjoyed otherwise. Speaking of nuance, many of the film’s scares transcend the peek-a-boo nature that plagues so many PG-13 horror offerings, and benefit from the film’s general awareness that sometimes, something simply being out of place is a lot scarier than all the abruptly shrieking violins in the world.

That’s not to say that Mama totally avoids some of horror’s more common traps. Several subplots go nowhere, with one involving the girls’ estranged aunt particularly disappearing until an unintentionally comical payoff too late in the film. The presence of Dr. Dreyfuss (Daniel Kash), so prominent as the girls’ psychiatrist in the early going, is resolved too easily and with too much distance from the brunt of the action. (It doesn’t help that his eventual trip to the cabin steals a scare tactic from the first Saw film.) The film’s climax manages to deliver a fairly poignant sucker punch while also verging precariously on the absurd, making a plot choice that the film wisely doesn’t attempt to explain before its conclusion. It’s a rather taboo turn, and even if it ends almost immediately after with too treacly of a final note, it perfectly fits with Mama’s position, just to the left of the standard center. And that’s a good thing.