Mara simply does not sustain narrative tension.
There are several overlapping sub-genres within the broader category of horror films: supernatural, psychological, slasher, gore-fest, monster and on and on. Every horror fan would probably compose her own unique set of categories, but also understand that there are distinct types within the genre. What is important is that a film know its niche and inhabit it as fully as it can; otherwise, it must be either transcendently outstanding (think of Get Out) or it will fail to really amount to much. Sub-genres aid narratives into coalescing into something that is suspenseful and engaging. Mara is precisely the sort of ‘tweener that does not come off, trying to carefully skirt the frontier between procedural thriller, supernatural horror, psychological drama and a few other horror sub-genres. Such imprecision makes it feel caught in-between rather than novel, more tedious than scary and both too-much-of and too-little-of each of the tropes essential to its array of sub-genres. It tries to be X and Y and Z, but instead is none of them.
Kate (Olga Kurylenko) is a psychologist/criminal investigator called in for her first assignment, a perplexing case of a husband horrifically murdered in his sleep and his stammering, out-of-her-head wife Helena (Rosie Fellner). The police—portrayed throughout as myopic and incompetent—jump to the obvious conclusion that Helena killed her husband. Kate is uncertain, but is intimidated into complying, setting up cycles of guilt for her, the couple’s young daughter and the now-detained wife.
From this exciting set-up (which also includes unfulfilled allusions to Southern gothic stylings), Mara drops the crime genre trappings (and the Southern gothic stuff, too) and moves into horror. It turns out the murdered husband suffered from sleep paralysis and was a member of a support group for those suffering from the condition–and other members of this group have recently been killed in the same fashion. Kate embeds herself in the group and discovers Dougie (Craig Conway), a violent ne’er-do-well who berates his fellow participants and guarantees more of the members will meet grisly ends very soon. Even the bumbling police find Kate’s evidence against Dougie compelling enough to release Helena from custody, but…it is too late. She, too, has been brutally murdered in her sleep.
It seems that some metaphysical evil is responsible for the killings, but what 21st-century detective would believe such a thing? In a world ruled by the scientific method and rationality, the actual murderer—an immaterial devil named Mara—is dismissed as the twisted, culturally-specific hallucination of sleep-deprived, broken people. The film again shifts, as Kate works to puzzle together how the psychopathic demon operates. How does Mara select victims? What explains the slow descent of certain people into sleep paralysis, madness and eventual gruesome death? And, most importantly, how to convince a broader, skeptical public of its existence?
The constant shifting in the narrative focus and even genre stylings of Mara works to dampen the tension. The film consistently gives the audience answers rather than keeping viewers on the hook. Instead of employing red herrings, partial explanations and various other narrative chicanery to ensure that viewers remain tuned in, the film constantly solves the puzzles it presents and then hopes to keep viewers engaged by introducing yet another puzzle. As a storytelling strategy, this approach could work, but usually only in serialized format. And given the predilection for horror films to rely upon a final-act big twist, storytelling in this genre often involves a last-minute solution to a puzzle that the audience did not even know was a puzzle; think of The Sixth Sense as a paradigmatic example. Director Clive Tonge defies such storytelling techniques, to his film’s eventual detriment. Most viewers are likely to simply check out because the film simply does not sustain narrative tension.