A tragic occurrence at the beach leaves Molly devastated and in need of professional care. After an indeterminate period inside a mental health asylum, she’s released back into the world and fixed up with a new apartment. But as Molly tries to piece her life back together, a persistent knocking coming from her ceiling – accompanied by the occasional whimpering – persuades Molly that a woman is being held captive and possibly tortured somewhere in her building.

Upon checking it out, the upstairs neighbours seem nonplussed at best and shifty at worst, with Molly unable to prevent her suspicions from falling on any of them. What’s worse, the police are entirely unhelpful and given her recent struggles, no one seems to give any credence to Molly’s claims or care about the fate of the mysterious woman who may or may not exist. Is it all in her head? As an unprecedented heatwave pushes the mercury ever higher and everyone around her tells her she’s crazy, Molly is in serious danger of losing her grip on reality.

This tightly coiled thriller from Frida Kempff is a fascinating case study of how a history of mental health issues can continue to afflict those affected, even after they have ostensibly recovered from their illness. The pacing is expertly managed, never too slow to lose the audience’s attention, but never too fast that it feels forced or unfeasible. Despite belonging to the “Midnight” strand of Sundance and being billed as a horror in some quarters, those seeking the thrills and jump-out-of-your-seat moments associated with the genre may be left disappointed. Instead, it’s a slow burn of a character study that you can never take your eyes off as Molly struggles to save the source of the knocking and her sanity in the process.

Sometimes, the turn from the lead actor enhances a film; at others, the central performance is the film. Knocking is one of the those occasions. While the thematic ground covered by Knocking is nothing ground-breaking and an astute observer might anticipate the plot turns well in advance, Cecilia Milocco is utterly enthralling as the harried Molly. That’s equally applicable when she’s playing the reformed patient shyly asserting her recovery, the amateur detective hell-bent on rescuing an abuse victim or – aided by some exquisitely intense in-your-face camerawork – the unpredictable loose cannon in danger of injuring herself or others in her quest for righteousness.

With its carefully measured pacing, credible narrative and excellent performances across the board, Knocking is far more than a mere spine-tingler. It might sit uncomfortably alongside others in the horror canon, but it’s a superb thriller with a lot of questions to ask about the stigma surrounding mental health. A masterpiece of suspense and self-doubt.

Screened as part of Sundance Film Festival 2021