Edward Jessup, a psychologist from Columbia University, is deeply fascinated by the enigma of schizophrenia. He begins to hypothesize that our subconscious might be as tangible and influential as our conscious experiences. This curiosity leads him to experiment with sensory deprivation through flotation tanks, alongside his colleagues, Arthur Rosenberg and Mason Parrish. During a faculty gathering, he crosses paths with Emily, a dynamic intellect who eventually becomes his life partner.
As years roll by, Edward’s professional pursuits mirror the turbulence of his personal life. His marriage to Emily hangs in the balance, yet they are tied together by their mutual thirst for knowledge. When Edward comes across the Hinchi tribe, known for their ritualistic collective hallucinations, he journeys to Mexico to immerse himself in their sacred rites. Upon reaching the enchanting Hinchi hill country, adorned with mushroom-shaped rocks, he meets Eduardo Echeverria, his supportive guide.
The elder of the tribe, known as "the brujo," entrusts Edward with a mystical potion made from the legendary Amanita muscaria mushrooms and the enigmatic shrub Heimia salicifolia, lovingly dubbed the "first/primordial flower." This plant is believed to invoke profound memories and heightened states of consciousness. As Edward clutches a root from the revered shrub, the brujo adds drops of his own blood to the mix. Soon, Edward is plunged into a chaotic and vivid hallucinatory state, inundated with visions of decay and erosion, swirling in sandstorms with Emily.
The following day, Edward departs from the Hinchi plateau, now clouded in moral turmoil after unintentionally killing a sacred monitor lizard while under the potion's influence. The weight of this act manifests in his dreams, where a petroglyph symbolizes the gift of the sacred mushroom tied to the tribe's mythology.
Back in the United States, Edward, fueled by an insatiable quest for knowledge, begins to analyze the Hinchi potion, eager to dive deeper into the intricacies of human consciousness. However, the potion's potentially perilous effects mount with every intake, leading him to retreat into sensory deprivation with hopes of enhancing the substance’s potency. In a makeshift tank within a medical facility, Edward embarks on increasingly shocking and disorienting visions, transporting him to the dawn of humankind and allowing him to witness early Hominidae. Even as his colleagues monitor closely, Edward claims these intense experiences have transcended into an "externalized" realm. Upon emerging from one session bloodied and frantic, he insists on undergoing X-ray imaging, leaving the radiologist baffled to discover they belong to a gorilla.
As his explorations deepen, Edward encounters even more surreal phenomena. He emerges from the tank resembling a feral caveman, driven by primal instincts, causing chaos before reverting back to his human form. Undeterred by the unease of his associates, Edward perseveres, fueled by an unrelenting desire to explore his self-evolution. In one last act of desperation, he plunges into the depths of his psyche, transforming into a formless, sentient mass of primordial energy. The aftermath of this experiment sends shockwaves, incapacitating his colleagues and obliterating the tank. When Emily, who is observing this decline, arrives at the scene, she only finds a torrent in place of the tank and desperately searches for Edward, who teeters on the edge of disappearing into a void.
With support from friends, Edward is safely returned home, as they anxiously await the conclusion of his metamorphosis. With Emily's watchful gaze upon him, Edward's regression continues unabated, demanding neither the mystical brew nor sensory isolation. As Emily pleads with him to resist this unraveling, she reaches out and takes his hand, only to be ensnared by the swirling primordial energy radiating from him. This jarring moment ignites the flicker of humanity within Edward, compelling him to resist the transformation. With a final surge of will, he reclaims his human form, embracing Emily, who too has regained her normal self. Their love shines brightly, a beacon guiding them out of the dark abyss that nearly consumed them both.
