While the mainstream film industry wrestled with the restrictions of the Covid crisis, the horror genre offered creative opportunities for those willing to take risks. Last year saw the writing, filming and release of Rob Savage’s Host, a brilliantly stripped-down online seance chiller, tailor-made for home viewing. Meanwhile, High-Rise director Ben Wheatley went the other way, conjuring a widescreen outdoor fiesta (written during the first lockdown and shot quickly last summer) that plays like a mashup of the 15th-century Malleus maleficarum and Merlin Sheldrake’s mycelium-themed 2020 book Entangled Life – all reimagined as a trippy horror movie. A modern-day companion piece to Wheatley’s eccentric 2013 civil war film A Field in England (complete with shroomy visions and tethered rope walks), it could well have been called A Forest in England. In a world blighted by a deadly pandemic, Martin Lowery (Joel Fry) joins park scout Alma (Ellora Torchia) to make a Blair Witch-style trek into British woodlands. They’re set to rendezvous with Dr Wendle (Hayley Squires), a renegade scientist investigating how the plant life is linked underground, like a giant brain. But this latterday Hansel and Gretel are not alone, with ominous traces of disappeared fellow travellers suggesting that something wicked this way comes. Is someone in the forest watching them? Or is it the mythical woodland spirit of Parnag Fegg? To reveal much more about the plot, which channels everything from Algernon Blackwood’s early 20th-century novella The Willows¸through the Nigel Kneale-scripted 70s gem The Stone Tape, to Alex Garland’s 2018 Annihilation, would be to spoil a delicious element of discovery. Suffice to say that, as with all of Wheatley’s best works, In the Earth combines humour and horror in terrifically bamboozling fashion, not least during a gruellingly extended amputation sequence that will have you squirming, laughing and wincing all at once. Elsewhere, Cyriak Harris’s spiralling animations combine with inventive in-camera visuals (plaudits to production designer Felicity Hickson and cinematographer Nick Gillespie) to prove that, as Reece Shearsmith’s bewitched hermit Zach observes: “Photography is like magic.” Wheatley previously flirted with the trappings of British folk horror in Kill List, a thriller that slipped unexpectedly into outlandish Wicker Man-style pagan ritual. Here, he builds upon the monochrome experiments of A Field in England to conjure immersively colourful explosions of sight and sound, reminiscent of the glorious visionary excesses of Ken Russell’s Altered States. You can almost hear Wheatley cackling with glee at some of the movie’s most outlandish sequences, with Clint Mansell’s gorgeous, giallo-tinged score intertwining with Martin Pavey’s throbbing sound designs, like some vast sonic mycorrhiza. The result absolutely demands to be experienced on the biggest screen possible in a darkened auditorium with the sound turned up to 11, engulfing the viewer in its deliciously dark spell. At times I was reminded of the off-kilter eco-themes of sci-fi writer John Wyndham, not least in a wonderfully heady sequence in which the forest traps its human visitors with a mist of mushroom spores. There are hints, too, of the retro-70s pastoral gothic seen recently in the Canadian cursed-film mockumentary Antrum, in which gateways to heaven or hell lurk amid the foliage of unearthed celluloid. Yet whatever the tangential comparisons, In the Earth is unmistakably the product of Wheatley’s uniquely fetid imagination, an imagination that has grown like a psilocybin-rich fungus upon the steamy inspirational midden of Nicolas Roeg and John Boorman, filtered through an apprenticeship in viral comedy and a long-standing love of anarchic dystopian horror. From here, Wheatley is off to film the “Jason Statham shark-puncher” romp The Meg 2 (I cannot wait to see what he makes of that!). In the meantime, this joyously mischievous film serves as both a timely response and an unruly retort to the strictures of lockdown, a breath of frightening fresh air with a pantheistic sting in its tail.