SEEING is deceiving in Steven Soderbergh’s hallucinogenic mind trip for a traumatised data analyst, who sees the menacing face of a stalker everywhere she turns.

Scripted by Johan Bernstein and James Greer, Unsane is shot entirely on a smartphone and generates sparks of claustrophobia from the restricted screen framing and occasional blurring of images as characters race around dimly lit corridors.

In his capacity as director and editor, Soderbergh loosens his usually firm grasp on the film’s quickening pulse as boundaries between reality and nightmarish imagination blur with violent consequences. Shaky handheld camerawork has a verite, improvised quality akin to a fly-on-the-wall documentary rather than a studio-financed psychological thriller.

Stockport-born actress Claire Foy convincingly casts off the pomp and ceremony of her award-winning role in The Crown to play Sawyer Valentini, who has moved from Boston to Pennsylvania to escape the barrage of text messages of a mentally unstable admirer called David Strine (Joshua Leonard).

Always looking over her shoulder, Sawyer searches online for support groups for victims of stalking. She is directed to Highland Creek Behavioural Centre, where trained staff will apparently diagnose the best course of action.

Filling in a series of forms to complete her treatment, Sawyer is shepherded into the depths of the facility, where she discovers that her hastily scrawled signature has condemned her to a living nightmare.

Sawyer is forcibly relocated to a dormitory and, as she queues for medication, she is horrified to discover that another nurse bears a spooky resemblance to David. Could he have cunningly infiltrated Highland Creek or has she finally lost a hard-fought battle with delirium?

Unsane sacrifices deep and satisfying character development to explore the freedom that smartphone technology grants an Oscar-winning filmmaker, who can now get uncomfortably close to his protagonists in confined spaces – both real and imagined.

Once the script commits itself to revealing whether the terror is only in Sawyer’s muddled head, tension dissipates and we’re left with a freewheeling piece of genre filmmaking that unsettles but never chills.

RATING: 6/10