Gabi and Winston, employees working for South Africa's forestry service, embark on an expedition along a river in the picturesque Tsitsikamma forest. During their journey, Gabi has an unfortunate mishap and loses the control of her drone. Determined not to leave behind any waste, she bravely decides to venture into the depths of the forest alone to retrieve it, saying: > "we can't just leave our trash here."
As she traverses the woodland, Gabi inadvertently activates a hidden trap, resulting in a painful wooden stake piercing through her foot. After extracting the stake, she pushes farther into the forest, where the scenery transforms under the ominous red glow of nightfall. Eventually, she discovers an isolated wooden house and enters it to tend to her injury and recuperate.
Inside the house, she is unexpectedly joined by Barend and his son Stefan, two survivalists who had made the house their home. Aware of her predicament, they attend to her wounds. Meanwhile, Winston, hearing Gabi's anguished scream as she removes the stake, sets out to find her but to no avail. As darkness envelops the woods, he encounters bizarre creatures and becomes infected with a swiftly spreading fungus while attempting to hide from them.
As the story unfolds, Gabi shares a growing bond with Stefan. She soon becomes plagued by terrifying nightmares involving fungi sprouting from her body, discovering patches of the growth on her limbs. Barend reveals haunting details about his past, sharing that he was once a plant pathologist. He retreated into the forest following the death of his wife Lily to bone cancer thirteen years prior, and that Stefan was born in the very house where he and Lily celebrated their honeymoon. He cryptically mentions that he "met God" while living in the forest.
One night, while Gabi is vulnerable in sleep, she nearly falls victim to the encroaching fungus, but is saved by Barend just in time as the creatures attempt to break into their sanctuary. When the creatures invade, Gabi and the audience unmask their true identity—they are ordinary humans, but covered with a mass of fungi. Barend clarifies the terrifying nature of their existence, explaining how the fungus infects humans, preying on essential parts of the body and spreading through spores. He elaborates chillingly on the presence of the largest organism on Earth nearby, ominously asserting: > "She was here long before the apes started dreaming of gods."
After a tense night, Gabi stumbles upon Barend's writings that reflect his cynical view of humanity, comparing them to monkeys in captivity. Barend participates in strange rituals, offering gifts to a tree that houses the colossal organism. In the midst of this surreal journey, both he and Stefan consume some of the unusual mushrooms growing on the tree. Their expedition takes a dreadful turn when Gabi finds Winston's flashlight, leading them to a shocking discovery—Winston, now entirely covered with various fungi, desperately pleas for death. Barend almost succumbs to the stress and prepares to finish Winston off, but Gabi intervenes, leading to a grim impalement as Winston himself resorts to self-harm.
Amid the chaos, Stefan secretly offers Gabi one of Barend's mushrooms. The narrative darkens further as Stefan takes Gabi to witness his mother, who has tragically transformed into a grotesque animate tree, still wearing her wedding ring. Gabi's horror deepens as she goes through captured images from a camera earlier used in the forest, revealing disturbing truths about the creatures haunting them.
As tensions rise, Gabi and Stefan head toward the city, only to confront Barend once again. He manipulates Stefan into staying deep in the forest. Ultimately, Gabi stands at a crossroads, initially retreating to the city alone but then, driven by a desperate need to protect Stefan, she makes a last-minute decision to prevent Barend from sacrificing him. In the ensuing struggle, Stefan succumbs to the darkness and stabs Barend in the back, who subsequently becomes a vessel for the growth of fungus.
Time passes, and Gabi finds herself infected, her body overwhelmed with the parasitic growth. In a moment of despair, she pleads with Stefan to end her suffering, which he appears to do. Ultimately, Stefan leaves Gabi's lifeless form behind in the house and heads toward the city where, post-meal, he observes that even the leftovers from his meal are soon engulfed by gnarly fungi.
