As the esteemed Professor Howard Birack (Howard Birack) and his students embark on their journey to the ancient Saint Goddard's monastery, they are welcomed by a Catholic priest eager to divulge secrets hidden within the walls. This sacred place is home to the Brotherhood of Sleep, a mysterious order that shares knowledge through the realm of dreams. They request assistance in understanding a cryptic cylinder, which contains a swirling green liquid that appears to harbor mysterious powers.
Among the academic group of thirteen are Walter Fong, known for his sharp wit; Kelly, an enigmatic figure; Susan Cabot, intelligent and sensitive; the easy-going Mullins; and the couple Brian Marsh and Catherine Danforth, whose romantic connection adds depth to their exploration. Their adventure broadens as they are joined by fellow scientists Calder, Lisa Blount (Lisa Blount), Etchinson, Lomax, Frank Wyndham, and Dr. Paul Leahy.
Venturing further into the labyrinth of the monastery, the team uncovers an ancient text that discloses the liquid as the embodiment of Satan. The shocking revelations escalate when they learn that Jesus Christ may have been an extraterrestrial being, condemned for heresy after attempting to warn humanity about the vessel containing Satan’s essence. Analyzing surrounding texts with computer assistance, they come across complex differential equations that might unveil further secrets.
As time passes, small bursts of the sentient liquid escape the cylinder, and Susan suffers the first dire consequence as it invades her throat. Her subsequent metamorphosis into an unwitting instrument of malevolence is immediate, provoking a merciless pursuit of her friends. The horror escalates as Wyndham meets a brutal end at the hands of a homeless individual now under the cylinder’s sinister influence.
One by one, team members fall victim to the liquid's grasp: Mullins, Lisa, Calder, and Dr. Leahy succumb. Anyone attempting to flee is met with grim deaths, as a throng of entranced homeless encircles the monastery. Etchinson is confronted by the leader of this forsaken mob, culminating in a shocking act of violence. As despair sets in, the remaining team faces a heart-wrenching dilemma: surrender to the encroaching darkness or risk everything to escape the insidious force that threatens to consume them.
Immersed in the investigation, Professor Birack and the priest theorize that Satan may be merely a progeny of a more sinister entity—the Anti-God, a force linked to anti-matter. Meanwhile, the survivors grapple with haunting visions of a shadowy figure, a tachyon message from the future warning of impending doom. Each dream reveals more intricate details of a broadcast from 1999, hinting at an apocalyptic fate.
In a desperate effort to escape, Walter finds himself trapped in a closet, powerless as the cylinder is presented to a slumbering Kelly. The liquid infuses her body, morphing her into a terrifying vessel for Satan, endowed with telekinetic and regenerative powers. In her attempt to beckon the Anti-God through a compact mirror, she discovers the mirror is too small for her ambitions.
Pandemonium ensues as the possessed now turn against their former allies. Lomax is killed by Mullins, who has been overcome by the dark force. While chaos reigns, Kelly finally discovers a larger wall mirror and manages to draw the Anti-God's hand through it, forcing open a portal to another realm. The only unpossessed member, Catherine, confronts Kelly, hurling both women into the opened portal. The priest shatters the mirror with an axe, sealing Kelly, the Anti-God, and Catherine in an alternate dimension. As those under the liquid's thrall collapse, the frightened street people disperse, ushering in the rescue of the surviving scholars: Brian, Walter, Professor Birack, and the priest.
In an unsettling conclusion, Brian endures yet another haunting dream, confronting Catherine, seemingly under Satan’s control. This turn of events, however, is revealed to be merely a foreboding vision, ending with him awakening with a scream and reaching for the surface of his bedroom mirror just before the screen fades to black.
