Warning: This review discusses the plot. Please attend your nearest pagan festival before reading on.

Asi Aster’s Hereditary encore provides a useful checklist of things to avoid if you’re an inattentive boyfriend who wants to cut his dysfunctional and grief stricken girl loose but feels trapped – particularly after her bipolar sister complicates matters further by killing herself and murdering the ball and chain’s parents.

Be wary, says the movie, of your Swedish pal, also studying for an anthropology doctorate, who suggests taking you and your obnoxious friends on a field trip-cum-holiday to his isolated pagan commune for their secret and undocumented summer solstice festival. Be concerned that’s he’s particularly interested in your woman, especially when the subject of May Queens are discussed (though it’s June/July). Worry when you arrive and the group’s first move is to pump you with hallucinogenic drugs. Really start to worry when your friends slowly disappear following unintentional acts of casual cultural disrespect (understandably you think is all information about the festival and its antecedents has been carefully withheld), and get nervous to the point of planning an early morning escape, when a caged bear appears and no one will tell you how it fits into the festival.

There’s a very morbid joke at the heart of Midsommer that’s both audacious and jet black, and one has to commend Aster for seeing it through. Having decided that, in a riff on the Wicker Man that also acts as a demented feminist clarion call and sinister dig at ineffectual masculinity in a hedonistic culture (with a judicious drop of casual misandry – but hey, thanks the Hollywood trade off, kids), Dani will close the movie by choosing her man (who’s been groomed to inseminate a local virgin) for human sacrifice, adopting the group as her family as he burns – it’s necessary to work backwards and provide enough psychological shade to facilitate this brutal scenario.

Having boyfriend Christian (hint hint) have one foot out of the relationship is a good start; him not quite holding Dani as she grieves for her dead family, even better. And then there’s the slew of subtle vignettes – moments of emotional detachment that seal the deal – his compulsion to get his rocks off with the blaze-haired local girl because Dani, a depressive, won’t put out – forgetting her birthday, switching off when she speaks, not knowing how long they’ve been together and so on.

This, you intuit, is the careful laying of ground. By the time you realise where Aster’s going, the only question is whether he’ll have the balls to go through with it. Perhaps unsurprisingly, given Midsommer’s embrace of its pagan forerunner’s brutality and other influences, most notably the mallet welding violence of Texas Chainsaw Massacre, he does. And with that, the movie’s done its evil work. So alienated has Dani become, so detached from her lazy, feckless boyfriend and his self-important friends, that she’s ready to join the pagan sisterhood and forsake her old, miserable life. We suspected it when she didn’t react to the elders’ head smashing suicides, but still….

Midsommer’s a slow burn, but even there, in its careful roll out, its meticulous sensibility and sharp technique in the practice of building sustained menace, is a wonderful bit of self-referential humour that foreshadows that brutally funny ending. Aster’s direction is cold and artful – notes of Roeg and Kubrick that lend this superior horror-cum-black comedy an edge that many of its contemporaries lack.

It’s destined to become the go to movie for women disgruntled with their men everywhere. Come for the camaraderie amongst women and the floral dancing (only lapsing when they bury the London girl upside down in a flower bed), stay for the boyfriend in a bear skin. Oh Ari, you are a card.