Documentary-maker Frida Kempff makes her feature debut with a Swedish-set thriller drenched in urban paranoia. Molly (Cecilia Milocco), who has recently finished a stay at a psychiatric hospital following a personal tragedy, has moved into a new flat hoping for a fresh start. The plan proves futile: she is soon plagued by mysterious, relentless sounds of knocking coming from her ceiling. Convinced that someone is being hurt, Molly is determined to trace the origin of this mysterious cry for help, only to be faced with others’ disbelief and her own deteriorating sanity.

Such a premise is by no means novel – apartment angst has been done to death since at least the mid-60s, after Polanski’s Repulsion – yet the eerie visuals and Milocco’s heart-wrenching performance elevate Knocking above its otherwise thin plot. Set during a scorching heatwave, the film beautifully pairs the restlessness of the summer with Molly’s own wandering mind, which scissors back and forth between her claustrophobic present and sun-drenched memories of a former lover on the beach. Natural light only exists in these aching echoes of the past. Mostly shot inside Molly’s flat, the imagery is smothered in jaundiced fluorescent tones, only accentuating her isolation and worsening state of mind.

As Molly inches closer to the centre of the puzzle, Knocking ditches its slow-burn pacing and plunges viewers right in the midst of all-consuming hysteria via an outstanding sequence of body camera closeups. Without giving anything away, what starts out as looking like a quotidian thriller superbly coheres into a sensitive study of trauma and loss. Clocking in 80 minutes, the film still feels a tad long for the simple narrative it offers, but moments of visual ingenuity and a deep understanding of psychological suspense show that Kempff is one to watch.

• Knocking is released on 15 November on digital platforms.