Opening with a cheeky nod to the saccharine midcentury harmonies of The Sound of Music’s Von Trapp clan, horror import Goodnight Mommy is racking up raves for its slightly more menacing take on familial love and devotion in the idyllic Austrian countryside: What if the mother you loved wasn’t really your mother, but something utterly sinister posing in her skin?

Written and directed by aunt-nephew duo Veronika Franz and Severin Fiala, Goodnight Mommy alights on Lukas and Elias (Lucas and Elias Schwarz), 10-year-old identical twins who spend their days blissfully roaming the wilderness around their secluded lakeside home. When their TV host mom (Susanne Wuest) returns in bandages after undergoing facial reconstructive surgery, she shuts out the sunlight, orders silence in the house, and starts skulking moodily in the shadows.

The rambunctious boys are perplexed. Mystified by their mummified mom, the boys begin to wonder, poke, and prod. When she reveals her new visage to them, they launch their own skeptical interrogation. Where did that birthmark go? What color were Mother’s eyes again? Where did their real mother go?

The differences aren’t just physical. Something deep within Mother has changed. Her temper is now as swift as it is violent—quite unlike the old “Momma.” At times she cruelly favors one son over the other, forbidding Elias to speak to his brother. The boys begin to suspect that a malevolent imposter has replaced the warm and loving mother they once knew. “She’s not our mom,” they whisper in the dark, comforting one another.

Those whispers between brothers turn into demands as the increasingly suspicious boys resort to interrogation. “We want our mom back,” they tell her, only to be met with exasperation and anger. “You’re not our Mom!” Their father’s absence remains unexplained, although family portraits of the happy, dad-less trio adorning their austere, modern house suggest he’s been long gone.

Hailing from the land of unnerving auteur Michael Haneke (Funny Games, Caché), to whom it owes a spiritual cinematic debt, Goodnight Mommy cannily captures this disorienting universal nightmare from both sides as trust evaporates between everyone in play. Desperate to know the truth and save the mother they love, the boys raise the stakes by putting together a toolbox of terrifying household items. Scissors, tape, super glue, and a magnifying glass make for improvised torture tools as the filmmakers turn Brahm’s Lullaby into a sinister serenade.

Franz and Fiala deftly toy with their audience by shifting Goodnight Mommy from psychological thriller to true horror, and ratcheting tension from the twins’ perspective as the mother-child cat-and-mouse game escalates. The imaginative boys dream up several cringe-inducing adolescent torture tactics, pushing the film into even more ambiguous territory and posing the real quandary: Who’s the real monster here?

Puzzle pieces dropped into place here and there lead into a skin-crawling denouement so twisty, Goodnight Mommy begs an immediate second viewing. Parents with young children should find this, hands down, the most terrifying film of the year. As Austria’s official Academy Award Foreign Language entry, it could also turn out to be another kind of rarity: a horror flick worthy of an Oscar.