"Oculus" is not just a howling good horror film. It's a terrific film by any standard — a smart, character-driven, original hair-raiser that creeped the socks off me with no cheap scares. Watching the assured, nerve-racking theatrical debut of writer/director Mike Flanagan, I felt he'd put me on an icy IV drip of dread.

"Oculus" is a story that could be an account of supernatural happenings, or a story seen from the viewpoint of a lunatic. It's genuinely unpredictable. The key players are twenty-something Kaylie Russell (Karen Gillan) and her slightly younger brother Tim (Brenton Thwaites), reunited after his decadelong stint in a psychiatric hospital.

The siblings are still emotionally wounded by the violent deaths of their parents (Rory Cochrane and Ketee Sackhoff) 11 years earlier. Kaylie blames occult forces inside the Lasser Glass, a centuries-old mirror the family owned. She intends to prove it, rigging their childhood home with cameras aimed at the antique looking glass and persuading Tim to keep an overnight vigil with her. Tim agrees, in hopes of helping her banish what he sees as a destructive fantasy. The Newton Brothers' unsettling score and Michael Fimognari's ominous cinematography contribute to the aura of grotesque menace.

From its dark opening through its shattering endgame, "Oculus" keeps you guessing, off-balance, worried. You're never certain whether a paranormal entity is present, or if the deeply troubled siblings are descending into madness. Flanagan creates a remorselessly malignant atmosphere, shuffling past and present, memory and imagination in mind-bending twists that recall "Memento" and "Inception." He has clearly studied the masters of suspense and learned well. Form an orderly line, horror fans. A new classic has arrived.