There’s something about having an unreliable protagonist which breeds such engaging cinema. Dating back to Nikolai Gogol’s Diary of a Madman, it’s adopting the perspective of an unpredictable narrator, allowing the viewer to question what it is they’re seeing – and it’s here Steven Soderbergh’s Unsane comes into its own. With strong acting performances brining this tale to the life, it does beg the question – why did this esteemed filmmaker shoot this movie on an iPhone and thus undermine and cheapen his own storytelling credentials?

Claire Foy plays Sawyer Valentini, the victim of a stalker, who moved state and changed jobs in a bid to start again, away from her perpetrator’s unrelenting behaviour. Though she can’t escape him psychologically, and so she heads to a nearby hospital to talk a support group worker, and when asked if she ever feels suicidal, her elusive answer means she is involuntarily admitted into a mental institution. Pleading with the authorities that she’s completely sane, when she believes her stalker has taken a job at the building to get closer to her, her erratic behaviour convinces the doctors she’s rightfully being detained, as we’re led to wonder whether her claims are genuine, or if it’s all in her head.

Soderbergh has shot this movie entirely on an iPhone, and while this does enforce the voyeuristic nature of the production, not to mention the familiarity behind the aesthetic of the smart phone’s camera that enriches the authenticity, it still proves to be a detrimental move by the director. Unsane carries a strong, elusive narrative and contains several impressive performances – including that of fellow patients Nate (Jay Pharoah) and Violet (Juno Temple) and yet their efforts are devalued by the film’s shoddy presentation. It looks like it’s been shot on an iPhone – and that, sadly, isn’t a compliment.

Thankfully the ambiguity in the middle act helps to distract us from the visual experience, while Foy is terrific in the leading role, bringing a sense of volatility the characters needs, and a vulnerability that is equally as essential, as we strive to determine whether she is in fact a victim of an insurance scam, only detained so the institution receives a pay-out, or whether she’s genuinely suffering from a breakdown. There is something so endearingly, and inherently English about the actress, and with that in mind she’s really shown off her talents here, for while it had been hard to envisage her in the role of an American, since seeing the film you simply can’t picture the role belonging to anybody else.

Narratively the film does lose its way somewhat, and while the set-up and overall premise is a fascinating one, it suffers from a disjointed, overly-dramatic conclusion, emblematic of a film with a great idea that had seemingly been concocted without any real sense of closure, as we fall back on, and abide too stringently to tropes of the horror genre in the latter stages. This just feels too generic in a film otherwise thriving in originality.