Traumatised by horrors from her childhood, feisty twenty-something Allison Belle has been through the mill of incarceration, counselling and medication as she has continued to battle mental torment. Frustration and anger has led Allison to countenance ever more radical forms of therapy that might enable her to finally overcome the fears and anxieties that are crippling her life.

This decision leads her to sign up for the no-limits personal terror experience offered by Perdition. Their services guarantee to push you to your psychological limits, forcing you to confront your most deep-seated fears by signing over control of your mind and body – albeit temporarily – to the horrormeisters now in charge of you.

Those “submission” scenes are an intentionally uncomfortable watch, as new independent horror Extremity immerses the viewer in its harrowing world. Having Allison paired with fellow scare-seeker dude Zachary helps to prevent those early sequences from drifting too close to the voyeuristic, and while there are sexualised moments along the way, none are graphic and there’s very little nudity.

Perdition provides a strong premise for what in the hands of many indie-filmmakers would support a series of ever-more ghoulish set-pieces depicting the mental disintegration of its now regretful subjects. Extremity delivers just those kind of inventive, flesh-creeping horrors, and executes them with no little style. But there’s much more going on here than the familiar beats of scream-and-slash.

Flashbacks to Allison’s abusive childhood, troubled adolescence and fraught adulthood mean that her character is revealed as more of a resilient survivor than a helpless victim. With the terrors of the facility established, the film then goes behind the scenes of the operation to bring its cast and crew into plain sight, humanising the ghouls and monsters behind the masks, the CCTV and the fiendish remote-controlled nastiness.

The script by David Bond and Scott Swan blends the shocks, gore and plot twists with a knowingness about the genre that entertains rather than irritates. “You have a website and a YouTube channel. How scary can you be?” asks Allison during orientation. Later there’s a fantastic Planet of the Apes gag that’s a welcome respite from the growing darkness of the subject matter, but this remains a full-on horror flick that pulls few of its dramatic punches. It’s unnerving, unformulaic, and reveals its hidden secrets with both pace and ingenuity.

Relative newcomer Dana Christina (Wynonna Earp) is great as the emotionally and psychologically damaged Allison, a character bursting with self-doubt; a horror-buff desperate to exorcise her own demons, whose edge-of-sanity therapy drives her to some unexpected destinations. Sound textures, cinematography and set design are all impressive, with the threat of claustrophobic confinement a very effective recurring motif.

There are weak spots. The idea that these unspeakable experiences might “cure” a sufferer of their mental ills (rather than reinforce their PTSD or psychosis) is plain bonkers. The Japanese TV crew filming proceedings also seem superfluous.

But in contrast to so much derivative “maniac-with-a-machete” indie-horror output, Extremity displays a determination to do things differently and an assuredness and confidence that sets it apart. “Horror is no better than pornography”, charges Allison’s therapist. “It’s smut, dressed up as entertainment. It serves no greater purpose”. Whatever you think of that accusation, sometimes doing it really well can be purpose enough.

EXTREMITY / CERT: TBC / DIRECTOR: ANTHONY DIBLASI / SCREENPLAY: DAVID BOND, SCOTT SWAN / STARRING: CHAD ROOK, DANA CHRISTINA, J. LAROSE / RELEASE DATE: 2ND OCTOBER