Sleep TightSleep Tight sees Spanish writer and director Jaume Balagueró step back into the stoplight without [REC] co-director Paco Plaze with a markedly different kind of horror film – one set to a slower pace and removed of all-out carnage. The result is a masterclass in suspense that’s likely to send shudders down its baying audiences’ spines as screenwriter Alberto Marini touches on a nerve as he asks the unsettling, yet unspoken question of what happens when you’re asleep.

César (Luis Tosar) is the mild-mannered concierge of an upscale apartment building. He doesn’t have much contact with the residents, aside from those who set him mundane tasks and Clara (Marta Etura), the woman he’s somehow hellbent on making miserable. Each night, he slips into her apartment, drugs her and sets about terrorising her life as a form of unexplained revenge. His efforts are complicated, however, when Clara’s boyfriend returns, forcing him to be more cunning in his sinister venture.

Balagueró and Marini throw us headfirst into the narrative as we’re immediately forced to view everything exclusively from César’s prospective. It’s a method that harks back to a more traditional time of horror filmmaking in that it restricts what the audience sees, thereby establishing a state of unease right from the start. At first, César’s actions seem almost calls for attention, but as his determination refuses to falter, it becomes clear that his motivation to cause distress is emanating from a deep-seated place.

The reasons provoking his actions are kept vague (the reveal itself is worth keeping quiet to ensure maximum distress is achieved), yet the slow-burning, methodical way in which the narrative plays out – almost in sync with César’s own operation – results in complete captivation on the audiences behalf, even though what he’s doing to Clara is deplorable at best. Tosar acts this superbly, conveying César’s resoluteness with a disciplined brutality that stems from somewhere deep within.

Balagueró direction mirror’s César’s dexterity perfectly, so when César wavers, so too does the camerawork, giving us a good idea of how mentally unstable he is. This provides little comfort though, as César is clearly used to these lapses, and is quick to change his tactics to ensure he remains one step ahead of Clara at all times. That is, however, until Clara’s boyfriend arrives back on the scene and César’s plans slowly crumble, leading to a final act that very much worth the wait.

With the opposing personalities of César and Clara providing a neat contrast between his knowing insolence and her negligence, Sleep Tight is one of the most captivating, unsettling and tormenting thrillers of recent years. Balagueró, by centring his attention on a mentally unstable voyeur, has recaptured the masterful suspense achieved by only a handful of directors before him. What we have here is an original horror – one that should be admired for its willingness to put its audience through a truly terrifying ordeal.