CLEARLY director Steven Soderbergh doesn’t know or care about the meaning of the word retirement. After announcing he was bowing out of the directing business just a few short years ago, he burst back on to the scene with last year’s hilarious “Ocean’s 7-Eleven” heist comedy Logan Lucky.

And now, in true Soderbergh form, he has switched gears entirely for this peculiarly named, paranoia-soaked psychological horror-thriller shot on an iPhone. Yes, you read that right. But what may seem like a gimmick is actually a large part of the reason the film is so ruthlessly, under-your-skin effective. Get ready to feel uncomfortably part of this film’s world.

The plot centres on Sawyer Valentini (Claire Foy), a young woman who has recently tried to restart her life far away from the man who relentlessly stalked her. She has a new job, a new home and new friends, but she still understandably feels the traumatic psychological effects of his obsession that is beginning to cripple her newfound daily life.

After a much-needed therapy session, she finds herself unwittingly and, to her mind, involuntarily committed for strict observation at a remote mental institution. Vehemently protesting against her supposed insanity to staff members, while also dealing with the unwanted aggressive attention of fellow inmate Violet (Juno Temple), she begins to fear her grasp on reality may very well be slipping as she believes her dreaded stalker is working at the hospital.

The psychology-themed thriller isn’t exactly brand new territory for Soderbergh, having made the star-studded Side Effects back in 2013. But where that film was made with a slick Hollywood sheen to coat the darkness, this is an unvarnished, scarily up-close-and-personal experiment with an enjoyably pulpy B-movie sensibility but also the thematic brains to back it up.

The decision to shoot the film on an iPhone 7 Plus really lends a tangible sense of queasy unease and voyeuristic urgency to this rollercoaster of an experience. It’s not pretty but nor is it meant to be. It’s rugged, abrasive and icky – all the things this sort of film needs to be.

Much like when David Lynch switched to digital for Inland Empire, you feel like this is a singular filmmaker gifting himself a new kind of freedom which results in an overwhelming cinematic atmosphere of deep distrust and excruciating paranoia.

Now that doesn’t mean that he and every auteur director should start turning to smartphones to showcase their vision for every film, but in this case it aesthetically helps to burn away the safety net we, as the audience, usually have of being able to generally trust what’s going on. Are we watching a delusional woman descend further and further into mental illness or is she right all along?

Foy not only upends preconceived notions audiences may have for her after prim-and-proper roles in the likes of The Crown, Wolf Hall and last year’s Breathe, but positively rips them into a thousand pieces. She thwarts in-built expectations with a sensational, all-or-nothing performance palpable paranoia atop understandable freaking out over what she consistently claims is false imprisonment and the will of a stalker now controlling her life within the confines of a psych ward.

It’s a horrifying situation either way – is it worse if she’s really crazy or that her stalker is back for more? And what does that fresh distress, in any case, do to compound what’s already damaged a person’s psyche? We’re ruthlessly chucked into the deep end of it all pretty much from moment one, given a warped lense to experience it and left with an uneasy feeling of paranoia that lingers like the trauma that it so astutely dissects.