Chloroform is a psychopath's best friend in Sleep Tight, though having unfettered access to the home of one's target doesn't hurt either. That's the cozy position César (Luis Tosar) has working as concierge of the hotel that's home to Clara (Marta Etura), a beauty under whose bed César lurks every night until he can drug her, infest her apartment with cockroaches, screw her, and then sleep beside her. César's habit of also harassing her with texts and letters seems like a knuckleheaded bit of overkill considering that it results in police involvement, but director Jaume Balagueró's film is nothing if not a well-executed bit of escalating craziness. Crafted with the same patience exhibited by its protagonist, the story initially seems like the work of someone who wants it all to be taken at least semiseriously, with César's machinations detailed with borderline-plausible meticulousness. Once Clara's boyfriend reappears in the picture, however, Sleep Tight takes a steep dive into the wacko and is all the better for it. Stripped of any pretenses of "realism," the material — bolstered by Tosar's creepazoid nastiness — spirals in increasingly loopy ways, with the only thing more preposterous than César's master plan being his contentious relationship with a blackmailing preadolescent girl (Iris Almeida) who almost matches his amorality.