Gruesome violence and grisly backwoods “surgery,” blood and stitches and axes and arrows, sharp stone shards left as booby-traps for the unwary dominate “In the Earth.”

Kind of what you’d expect from a thriller built around mycorrhizal research deep in the forests of Britain, eh?

The pandemic picture from the director of “Free Fire,” “High Rise” and “Sight Seers” goes back to that earliest film, just in terms of setting and simplicity.

A contagion is decimating the planet. Scientists are looking for cures, scouring nature in search of medicinal plant life. But one scientist in particular is onto something even more amazing.

Joel Fry stars as Martin, a researcher who has trekked to Gantalow Lodge in Britain’s woodlands to pitch in. It’s been turned into a research station, with rigid testing/disinfectant protocols, the works. And that’s just getting in the door. Martin is must be guided, on foot, deep into the forest to meet a former colleague. Dr. Wendell, encamped two days walk away, hasn’t been heard from in months.

Another researcher, Alma (Ellora Torchia) will be his guide. The virus that is killing people everywhere is still “outside,” in the cities and towns. But here in the woods, something altogether weirder is going on.

“People get a bit funny in the woods,” is one sage’s suggestion.

Foreshadowing? Let’s talk about the forest creature of local lore, “Parnag Fegg,” something Alma’s read a bit about. But when things go sideways on their hike — abandoned campsites, odd noises, a midnight mugging, help from a mysterious survivalist named Zach (Reece Shearsmith) — it certainly seems like humans devolving into animals in a societal breakdown is to blame.

Writer-director Ben Wheatley takes an almost sadistic pleasure in setting up and showing, in excruciating detail, the gory injuries and gorier “treatments” that these hapless city folk face in those spooky woods.

The conceit behind the picture is scientific up to a point, with some fanciful leaps and a trippy “explain it all, but not really” third act of murderous madness.

There’s a neat inversion of “types,” with the women of the story (Hayley Squires plays our reclusive, encamped researcher) responsible for driving the plot through their own agency. as we use the term in cinema these days. Fry’s Martin is passive in their presence.

There’s not an awful lot here, but this may be the best of the “pandemic” movies — science fiction and horror that is both “of” this moment, and a parable about it.

MPA Rating: R for strong violent content, grisly images, and language

Cast: Joel Fry, Ellora Torchia, Hayley Squires and Reece Shearsmith

Credits: Scripted and directed by Ben Wheatley. A Neon release.

Running time: 1:42