American student Tara and her college friends embark on an adventure to Ireland to reconnect with their local friend Jake. Their journey leads them to camp in the lush woodlands that surround an abandoned children's home, filled with an eerie history. During their exploration, while gathering psilocybin mushrooms for a later celebration, Tara mistakenly consumes a death bell mushroom (Galerina) which triggers a seizure. Following this, she begins to have vivid, dream-like trances, filled with ominous visions of events yet to unfold.
As night falls, the group gathers around a campfire, and while Tara takes refuge in her tent, Jake shares a chilling ghost story about the ominous children's home nearby. He recounts the tale of a violent, sadistic monk who sought vengeance against one of his charges for a past grievance involving his twin brother's death. This disturbing narrative sends Tara into further distress, amplifying her premonitions, where she foresees the gruesome fate of her friends.
The tension heightens when Bluto, an aggressive jock, has a heated argument with his girlfriend and the rest of the group. Ignoring the group's plan to share the hallucinogenic tea the next morning, Bluto drinks it solo and embarks on a terrifying trip that ends in his mysterious murder, seemingly at the hands of the vengeful monk from the children's home.
The following day, the group barely registers Bluto's disappearance and proceeds to consume the mushroom tea themselves. Under its effects, they become disoriented and lost within the woods. As the three women bicker and split up, Holly and Lisa meet a horrific fate, brutally murdered in alignment with Tara's unsettling visions, after encountering local woodsmen Ernie and Bernie.
Meanwhile, Jake and Troy search for Tara and find her on the riverbank. They instruct her to head towards the abandoned home to seek help. However, their intentions are thwarted when Troy seemingly meets his end at the hands of the monk while Jake narrowly escapes through a high window, injuring his leg in the process. As Tara discovers Jake, they attempt to flee but tragedy strikes again when he is brutally murdered while they pause to rest.
Eventually, Tara awakens to the sound of a Garda helicopter hovering above, marking her as the sole survivor of this harrowing ordeal. As she is loaded into an ambulance, her mobile phone unexpectedly rings, igniting a series of rapid flashbacks. It dawns upon her that the death bell mushroom not only altered her consciousness but led her to unknowingly murder her friends. Desperate and pleading for help, she turns to the paramedic. But the tranquility is shattered as the scene reveals her bloody hands clutching a pair of bloody scissors, suggesting that she has also killed the paramedic. The film culminates with Tara fleeing into the dense woods, leaving viewers questioning the depths of her madness and the haunting legacy of her ill-fated adventure.
