William Friedkin’s first horror film following The Exorcist is one of those films that appears to have been consigned to history. Whether because it had such a messy shooting schedule, or because Friedkin himself was so unhappy with the result, The Guardian seems to have passed out of the annals of horror collectors and fans. In some ways, that’s because its plot is, on the face of it, so preposterous, as well as so out of sync with what was happening in American cinema at the time. Turning his back on the slasher craze that was peaking in the late 1980s and early 1990s, Friedkin – along with Stephen Volk and Dan Greenburg – penned a story of a Hamadryad, or tree nymph, who becomes a nanny in order to abduct babies and sacrifice them to a magical tree located in the depths of one of Los Angeles’ many canyons. If that combination of California and Druid mythology sounds improbable, well, it is, but at its strongest The Guardian manages to transform that improbability into an asset, making for one of the most unusual horror films of the early 1990s as well as some of the most atmospheric and idiosyncratic moments in Friedkin’s own very varied career.

Of course, the complicated shooting schedule means that The Guardian also feels like several films in one. Yet that’s less jarring than it might be in another film, partly because of the dexterity of Friedkin’s direction – almost clearer in a project with so many moving pieces than it would be in a more auteurist piece – and partly because the fusion of Druidic and Californian imagery subsists on such a strong sense of incongruity and displacement in the first place. As might be expected from the premise, there’s a strong recourse to cultic, pagan imagery, as well as a highly stylised and plastic brand of horror that culminates with some spectacular prosthetic moments and produces a kind of dark fairy tale atmosphere. Indeed, at times The Guardian almost feels like a particularly dark children’s film, the kind of cautionary tale shot through with sadistically brutal strokes of fantasy that was so in vogue at the end of the 1980s. At the same time, however, there is a more naturalistic aesthetic at play – specifically, the melodramatic naturalism of the Lifetime television universe, whose films often revolve around just this fear of a babysitter or other interloper interceding between mother and child with some grotesque and heightened maternal gesture. In fact, the film was actually recut as a television movie, at which point Friedkin removed his name from the project, although that seems like an odd gesture in retrospect, given how perfectly he nails the particular eeriness and atmospherics of the Lifetime look.

What both these horror approaches share, however, is a fixation with the population and placement of trees within Los Angeles suburbia. Apart from Jenny Seagrove, who plays the nanny and dryad, there are only three main adult characters – Phil (Dwier Brown) and Kate (Carey Lowell), who play the main couple, and Ned Runcie (Brad Hall), their neighbour. In many ways, however, these are more types than characters, and exist more to heighten the mood. It makes sense, then, that Phil is a television producer, Kate is an interior designer and Ned Runcie is an architect “responsible for twenty-five houses in the canyon,” since between them they sketch out is a space that both televisual and domestic, full of glistening picture windows that create a profound sense of porosity with the world outside. As might be expected, that makes for a highly spatial film, with Friedkin spending lots of time just tracing out the contours of the two main houses, both of which are designed by Ned. In fact, if Friedkin leaves any distinctively “auteurist” trace on the film, it’s in the variety and ingenuity with which he turns this series of leafy, glassy interfaces – so precious to the Lifetime universe – into the substance of the film, building a kind of tone poem out of glass, wind and trees. Even inside, it always feels as if there is a cool breeze blowing straight from the depths of the canyons, creating an airy, billowy, buoyant, pregnant sense of space and paving the way for a hyper-mobile ending that gathers up cross-country driving, running and flying into a giant supernatural wind.

Yet, as in so many daytime telemovies, the eeriest time is the noontide quiet, which Friedkin paints full of subliminal reshiftings and resettlings of shadows on the wall, slight tremors and murmurs in the canopy outside – moments when a woman’s intuition comes to the surface, producing a dawning and inchoate sense that things are somehow not right. It’s at these moments that the film really nails its main subject matter – the paganistic, ritualistic elements of everyday suburban life – as all the nanny’s activities with the couple’s baby take on an ancient and primal quality against the profound stillness of Los Angeles suburbia in the middle of the day. Nowhere is that clearer than in the fisheye camera used to capture the baby’s perspective, which anticipates the creepiness of babycams and bends the child into a series of contorted, plant-like postures, drawing out her vegetative stillness but also imbuing her with a new capacity for agency that exceeds anything the parents can fathom.

That agency extends, in turn, to the entire flora of Los Angeles, all of which is imbued with a sapient power that renders it complicit with the dryad and her tree. Indeed, so much energy is bound up in the natural world that a natural disaster never seems very far away – there is a suggestion that earthquakes are somehow responsible for unleashing supernatural potential into the biome – as Friedkin conjures up an eerie LA pastoral in which it is the deepest, darkest recesses of the bush and the very bottom of the canyons where magic tends to gather. Even without the collusion between trees and wolves that emerges in the third act, that profusion of botanical motifs would seem to play to all the fears about the wild fringes of Los Angeles that were peaking in the wake of the droughts of the late 1980s, when extreme dehydration and starvation brought an unprecedented number of mountain and desert predators into the city limits. With Friedkin’s masterly touch, however, it feels as if the entire film takes place at the paranoid threshold between canyon and backyard, or between canyon and back window, as some more inexorably mythical and enduring sense of place continually intrudes upon the quarter-acre blocks of these archetypal suburbanites.

Among other things, that threshold makes for a version of Los Angeles in which we never really spend any time in or around cars. One of the first indications that something is not quite right with the nanny is that she “loves walking” – she walks for miles for miles – even or especially as there doesn’t seem to be any real direction or focus to her walking (she’s as happy to walk several miles to the nearest major boulevard as she is to spend several hours window shopping once she’s arrived). In that sense, The Guardian captures something of the strangeness of Los Angeles traversed on foot – a sudden awareness of natural topography – that peaks whenever the film approaches the mythical tree, which is so sequestered and secluded that it can only be approached on foot.

And, in some ways, that tree is the real achievement of the film. It would be so easy for this horror climax – a monstrous tree – to be ridiculous. In fact, even writing about it makes it sound ridiculous. It’s amazing, then, that it turns out to be so eerie, partly because Friedkin and the screenwriters seem to have made the critical decision to never fully anthropomorphise its gnarled and twisted trunk, instead divesting it of any discernible “face” or point of focus beyond the expressions of the babies that have been sacrificed to it, frozen into its limbs in quite horrific postures that make for an eerie juxtaposition with the apparently benign, graceful dryad. In other words, for all that the tree is clearly continuous and codependent with the dryad, they are never identified enough for her to feel like its face either, not least because she is never really presented as malicious, but just a bit over-motherly and over-protective. In that disjunction – between dryad, tree and human – lies the genius of the film, which is only enhanced by the fact that Friedkin refuses to visualise the tree in any categorical way at all. Resisting any stable or single angle of approach, the camera seems to be caught up in the windy movements that the tree itself generates, rendering its looming movements quite unpredictable and unsettling, until it almost feels like an allegory for the shifting, elusive centre of Los Angeles itself, impossible for any of the characters to ever get a hold of it.

The result, then, is one of the rare horror films about plants that really works, if only because of how hard Friedkin works to capture the utter otherworldliness and alterity of plants themselves as living things. As the screen fades out on the fantastic final shot, which guides us through a shattered window to the apparently endless undergrowth and flora of Los Angeles, it feels as if we’re in a similar place to the close-up of the suburban lawn that opens Blue Velvet. While David Lynch obviously had a different kind of control over his subject matter from Friedkin here, both films feel quite contemporary in the ways in which they bypass a human-oriented ontology in favour of a lifeworld that’s resolutely discorrelated from the primacy of our own personal and perceptual experience – and it’s in the deftness of that move that their horror and beauty lies.