The Blackcoat’s Daughter is the directorial debut of Osgood Perkins — son of Anthony — and it’s a mind-bendy little number that combines two of horror’s core elements: a girls’ boarding school and demonic possession. The thing about Blackcoat’s, though, is that it doesn’t utilize either of those things in the way you’re used to seeing them. There’s no go-for-broke exorcism, and no topless coeds running from a slasher-style villain. To call the story a slow burn would be a mischaracterization of the word slow. It’s more like a meditation or a waking nightmare, the kind you’re not actually sure is a dream at all until it’s over and you’re safe again. That makes the ending, in which Emma Roberts screams on a frozen road after decapitating two people and packing their heads away in a suitcase, kind of hard to parse.
The movie focuses on three girls — Kat (Kiernan Shipka), Rose (Lucy Boynton), and Joan (Emma Roberts). Kat and Rose both attend the Bramford School, and Joan is a mysterious drifter whose journey intersects with the other two. As the Bramford girls both wait for their parents to retrieve them for winter break, Kat’s pallor becomes increasingly sickly and her behavior becomes increasingly troubling. At one point, Rose finds her in a boiler room prostrating herself before a glowing furnace, and while Kat detaches from everyone else around her, she grows more and more fixated on Rose.
When the story cuts to Joan for the first time, we find her in a bus-station bathroom, trying to rip a medical bracelet off her wrist. All alone in the cold night, Joan is rescued by a kindly man who offers to drive her as far as he and his wife are going, which happens to be in the direction of Bramford. The closer Joan gets, the more disturbed Kat becomes, until finally she stabs Rose and two school employees to death before cutting off their heads and performing a ritual with them in front of the boiler-room furnace. In the midst of all this, the man giving Joan a ride tells her that she reminds him of his daughter, who died nine years before. He shows her a picture — it’s a school portrait of Rose!
Only at this point do we learn that Joan exists in a different timeline than Kat and Rose: Her plot is actually taking place nine years after the events shown at Bramford. And she’s never going to intersect with the Kat story line, because Joan is Kat: The Bramford scenes are her flashbacks to that time she was compelled by a demon spirit to murder a bunch of people. (“Joan,” we’re meant to assume, is the name of a woman she murdered during her escape from the mental hospital.)
In the final two scenes that feature young Kat, she’s caught with the severed heads by a police officer — who eventually shoots her when she refuses to drop the knife she’s holding — which lands her in a hospital bed strapped to the handrails. Bramford’s presiding priest visits Kat and performs maybe the lowest-key exorcism in all of movie history, and as a shadowy horned figure appears, Kat whispers, “Don’t go” — even though her body is her own again, her soul is still somehow attached to the dark figure. It’s presumably after this scene that young Kat is turned over to a psychiatric care facility where she lived for nine years. When grown Kat realizes she’s found Rose’s parents, she murders them, too, completing the dark assignment she was given as a teenager, and returns to the boiler room in the now-shuttered Bramford School.
The following morning we see Kat wandering a lonely road and, for the first time, capable of expressing emotion. Finishing off Rose’s family seems to have lifted the burden of her possession completely, and she’s finally confronted with the gravity of her crimes. At the start of the movie, young Kat had a vision of her parents dying in a terrible car accident, which means in addition to her now guilty conscience, she is totally alone (and, presumably, on the lam). Perkins followed Blackcoat’s Daughter with the Netflix original I Am the Pretty Thing That Lives in the House, and considered together those movies demonstrate two key things: As much as Perkins loves to build a story around slowly intensifying dread, he loves an unhappy ending even more.