LONDON—It’s The Secret Garden on LSD, and—just a few minutes into this mind-bending character study—it’s obvious that this is going to be a very bad trip indeed.

All the Gods in the Sky explores the desperate story of an industrial laborer, Simon, who is left to care for his severely-disabled sister after a childhood game with their father’s gun went horribly wrong.

They eke out an existence in what was once their parents’ grand rural home, no longer able to heat the place or prevent it from falling into ruin.

If you thought it was impossible to imagine the life-long torment of being responsible for an accident that would wreck the life of someone you loved, French director Quarxx is here to show you that you’re wrong. He has imagined it. And he’s brought it to the screen with a nightmarish intensity that will be hard to forget.

His devastating and surreal French-language film brilliantly harnesses the power of the horror genre to take you inside a mind that’s been twisted and warped by grief and guilt.

Hidden by layers of violence, sci-fi surprises and a profound sadness, lies a film with the same ultimately positive message as The Secret Garden, Frances Hodgson Burnett’s 100-year-old children’s classic about a child confined to a wheelchair. Allowed to fester in darkness, misery can envelop a soul but you should never count out the innate human desire for redemption.

“ As well as a fantastical reflection on what it means to be a full-time carer and the wretchedness of being cared for, there is also an intriguing exploration of serious mental health issues. ”

Don’t let that chink of light give you a false impression. This is French extreme cinema at its most extreme. It’s no plot spoiler to say that Quarxx appears unfamiliar with the concept of a happy ending, and under absolutely no circumstances should a child watch this movie.

The film is an extraordinary achievement, however. As well as a fantastical reflection on what it means to be a full-time carer and the wretchedness of being cared for, there is also an intriguing exploration of serious mental health issues.

We first meet Simon (Jean-Luc Couchard) in the factory where he is a skilled metal worker clad in blue overalls. He’s unkempt, but trusted and hardworking. Despite mental-health issues that have required a compulsory treatment order for antipsychotic drugs, he manages to hold down his job and care for his sister, Estelle.

There are moments of great tenderness as he bathes her and reads romance novels to his bed-bound sister. These vignettes come between bursts of rage as he struggles to cope with their bleak prospects.

Estelle is played by Melanie Gaydos, an American model who has been diagnosed with ectodermal dysplasia, a genetic disorder which prevents the growth of teeth, nails and hair. Quarxx explained that he was unwilling to cast an actress for the role who would have needed prosthetics. The result is striking; there’s an initial reaction to recoil as the brain adjusts to Gaydos’ unique profile, but as the film progresses, her beauty is revealed in a way that could never have been replicated by make-up alone.

This is unmistakably a horror movie—with flashes of the extra-terrestrial and supernatural—but the only real jump scare comes in an early scene that is so realistic it is repeated 15 times every day in the U.S. Two young children have found their father’s gun. The little sister, Estelle, demands that she be allowed a turn. As soon as she takes it in her hands, the result is both inevitable and utterly chilling. Bang. Her life is transformed.

Simon, who handed the deadly weapon to his baby sister, never recovers. After 20 years of repercussions, he is left screaming into the sky: “What more do I have to do?... When will you help me?!”

The sprawling fallout is too much for Quarxx to handle. But there is no doubt that he succeeds in plunging us into the tumultuous gun-ravaged alternate reality that faces hundreds of American families every year.