In a quiet Catholic boarding school for girls, St. Mark's, a sudden darkness erupts when one day Elizabeth, a diligent student, is studying on the third floor and is attacked by unseen evil forces. Father Drake rushes in to help, but the malevolent force is overpowering, and Elizabeth vanishes without a trace. The shock rattles the campus, and the school is immediately shuttered as worried families remove their daughters, leaving a sense of dread looming over the halls.
Five years later, the campus reopens under a stern and unyielding headmistress, Miss Pearce. Father Drake remains on staff, yet the tragedy has left him a shadow of his former self, a man who drinks at a bar rather than facing the past. Five troubled and unwanted girls—[Alex], [Mara], [Cecilia] (who is blind), [Leah], and [Connie]—are left by their families at the school, each carrying their own burdens and secrets. The rules are harsh, and the third floor, the scene of Elizabeth’s disappearance, is strictly off-limits.
On this rigidly controlled ground, the girls discover that they are not alone in their strange experiences. Cecilia and Mara dare to venture toward the forbidden third floor, and Miss Pearce’s swift punishment follows. Alex steps forward to take the blame, receiving a harsh caning in front of the others, a grim reminder of how the school enforces its order.
As the days pass, Alex begins to dream of Elizabeth being possessed by a demon, and unsettling phenomena ripple through the classrooms and corridors. The five girls discover that they each possess unusual, supernatural gifts: Connie is a conduit for spirit activity; Leah can pass through solid objects; Cecilia has second sight, an ESP-like power; Mara can heal recent wounds; and Alex wields telekinesis. These powers start to reveal a shared, dangerous bond that neither Miss Pearce nor the other adults truly understands.
The reality behind the haunting begins to unfold when Miss Pearce summons the girls to a pentagram on the third floor, and Connie appears to be possessed. The demon finds a vessel in Leah, who can now pass through doors, and Leah confronts Father Drake in a chilling confrontation. The demon is named Legion, and the struggle escalates as Father Drake attempts an exorcism while Leah uses her new abilities to threaten him with deadly force. Meanwhile, the girls—having translated Elizabeth’s journal, which surfaced after Connie’s possession—realize they must escape. They split up to search for the others: Mara finds Father Drake, Alex locates Connie, and Cecilia encounters the demon face to face.
A brutal sequence follows, where Cecilia is severely injured and Leah’s head is crushed with a heavy book. Legion then moves on to Cecilia and grants her “first sight,” intensifying the danger. Mara and Alex try to flee, but Miss Pearce locks them in and breaks Mara’s healing hand, a cruel blow that deepens the peril surrounding them. The shocking revelation shifts the motive of Miss Pearce—she is Elizabeth’s sister, and her purpose is to save Elizabeth from Legion.
With time running out, Mara and Alex hide in a bedroom and invoke Connie’s spellbook to construct a protective circle. Cecilia/Legion penetrates the circle only after using her own blood to bleed away the lines, and she possesses Mara. In a desperate ritual, Miss Pearce continues to chant, while Elizabeth’s body slowly appears and then vanishes again, a spectral reminder of the girl who started this nightmare. Mara pursues Alex, who is stabbed in the stomach before Miss Pearce pleads with Legion to release Elizabeth, only to hear that the deal was for five girls, not four.
Alex harnesses her telekinetic power to force Legion out of Mara and into Miss Pearce, driving the demon’s head through a crucifix. Exhausted, Mara collapses, but she heals herself while failing to save Alex in time. A tense moment unfolds as Mara encounters Virgil, a monkish figure who seems to roam the grounds in robes. Elizabeth appears, alive and greeting him as Father, only to witness Miss Pearce seize the moment and transfer Legion to him. Elizabeth’s scream pierces the air as the film ends, leaving audiences with a chilling, unresolved fallout that circles back to the very beginning.
The haunting at St. Mark’s leaves a lasting impression about power, family secrets, and the perilous intersection of faith and the occult, all carried forward by a cast of young women who discover that their hidden gifts come at a grave cost, and that some pasts refuse to stay buried.
