D: Mike Flanagan. S: Mike Flanagan, Jeff Howard. P: Marc D. Evans, Trevor Macy, Jason Blum. Cast: Karen Gillan, Brenton Thwaites, Rory Cochrane, Katee Sackhoff. UK dist (DVD/Blu-ray): Warner Home Video.

Multiple tragedy strikes the Russell family when the father, software designer Alan (Rory Cochrane), acquires a large antique mirror to adorn the wall of his study in their new home. Unknown to him, the mirror – known as the Lasser Glass – has malevolent supernatural properties, and has been implicated in the deaths of over forty people during the last three hundred years. The glass, it’s implied, takes a sick delight in driving its owners murderously, or suicidally insane, by twisting their perception of reality. As the tagline has it, You see what it wants you to see; victims have been found dead of dehydration, lying in a bath full of water, and only once has there been a recorded instance of anyone trying to destroy the mirror. After this single attempt, the failed vandal strides out into rush-hour traffic and is swiftly pancaked.

Soon after the mirror arrives, family life starts to deteriorate. Alan takes to spending hours alone in his study, becoming withdrawn and irritable. The two young children, Kaylie and Tim, are convinced there is a sinister woman, with eyes like mirrors, living in their father’s study. When wife Marie (Katee Battlestar Galactica Sackhoff) finds her husband’s notepad obsessively covered in doodles – the name Marisol, over and over – she chucks a paperweight at the mirror in a fit of pique. Big mistake. The glass gleefully torments her with images of herself, disfigured and decaying, and she promptly jumps from sane to nuts. After she tries to strangle Kaylie, Alan chains her to the wall of their bedroom and (now completely possessed by the glass) proceeds to torture her into a state of animalistic savagery – before releasing her again to attack the kids. During the ensuing ordeal, the mother and father are both killed – and after the cops nab ten-year-old Tim for the murders, he spends the next decade under secure psychiatric observation.

We learn all of these past events in an extended flashback, stretched throughout the film and cross-cut with the present-day narrative, focusing on the adult Russell children. On his twenty-first birthday, Tim (Brenton Thwaites) becomes eligible for release, now fully-cured of his “delusions” regarding the true events of that terrible night eleven years earlier. But his sister Kaylie (Karen Gillan) has spent the intervening time tracking down the Lasser Glass (sold at auction soon after the tragedy) and after she picks up Tim from the hospital, she shares with him her plan for revenge.

Through her auction-house job, she’s managed to acquire the mirror and has re-installed it back in the family home, empty since the night of their parents’ deaths. Kaylie has devised a foolproof scheme to draw out the evil spirits from the glass, and destroy them. From the ceiling above the mirror she has suspended a ship’s anchor, attached to a set of barbells; a “kill-switch” timing device has been set to release the weights and smash the mirror, unless it is manually reset by either Kaylie or Tim. If the mirror tries to kill them, it’ll destroy itself; ingenious. Kaylie plans to map the mirror’s radius of influence by positioning lamps and potted plants at fixed distances from the glass – when the plants start dying, or the lights burn out, they’ll know the spirits are on the move. Kaylie has also trained two camcorders on the mirror to record physical proof of the spirits’ existence, and thus exonerate her brother of the deaths of their parents. It seems she’s thought of everything – what could possibly go wrong…?

Oculus is, at base, a straightforward haunted-mirror yarn, wildly overcomplicated by tricksy, criss-crossing timelines carefully designed to throw viewers for a loop and cause them to wonder, finally, just which way is up. In this objective Oculus is mostly successful; acting as his own editor, Flanagan deftly interweaves the overlapping time-streams so we’re never entirely sure what we’re seeing, intercutting events from the present with reaction shots from the past, and vice versa. He also has fun using cuts as a premonitory device, not unlike Dario Argento in The Cat O’Nine Tails (1972); puzzling sights (a wall, seemingly punched with a jagged hole, is seen to be intact again in the following shot) can act both as flashbacks and flashforwards, producing an effect on the viewer that’s genuinely disorientating. Add to this numerous additional reality-distortions (induced by the mirror in “self-defence”) – busy dialogue scenes, conducted in seemingly normal conditions, are revealed later to have masked very abnormal actions – and you have a film which demands a higher-than-average level of concentration from its audience.

With its clever construction and complicated rules, the film seems at times like an ultra-scary episode of Doctor Who (Steven Moffat iteration), a connection encouraged by the casting of former Who-Girl Karen Gillan as its resourceful heroine. Unfortunately the parallels run closer than that, since the film’s plot could tidily fit inside a 45-50 minute timeslot – unsurprisingly, perhaps, since Oculus is a feature-length expansion of an earlier short film by the director (Oculus Chapter 3: The Man With the Plan). The tangled timelines and disorientation techniques sadly run out of steam before the film’s end, and the film ends on a glum and unsatisfying “surprise” downer that’s highly unlikely to encourage good word-of-mouth. This is especially disappointing, given the sustained tension and overall intelligence of Flanagan’s previous chiller Absentia (2011) – a film with a far more convincing grasp of character, not to mention a superior handle on its narrative ambiguities. (Like Absentia, Oculus offers non-supernatural alternatives to its spooky goings-on – but the impression here is of an idea half-heartedly grafted onto the plot, to be quickly abandoned.)

It’s not all bad news, by any means: Oculus is often heart-stoppingly frightening, with a solid (if unoriginal) basic setup and heroes you care for; Flanagan’s editing is superb; and the growling electronic score by The Newton Brothers is highly-effective at summoning dread. The reality-warps keep the viewer on his toes, at least until the disappointing finale, and often carry a genuine visceral punch. (A word of advice to would-be ghostbusters: if you leave a half-eaten apple next to a fat lightbulb, make damn sure which one you’ve picked up before taking a big crunchy bite.) With some extra fine-tuning of the key final act, and a rather less lugubrious style, Oculus could have been a minor classic; as it stands, however, it’s a dour and largely fun-free exercise in missed opportunities. For his next feature, it’s to be hoped Flanagan learns from this experience and really pulls out all the stops.