Martin, a somewhat unreliable water sanitation worker, stumbles upon a bizarre and fleshy organism inside a water treatment tank. Concerned about this strange find, he reaches out to Belinda Yost, the seller of unusual biological specimens at International Medical Specimens Inc. (IMSI). Her excitement upon hearing from Martin is evident, prompting her to rush out to meet him. Recognizing the potential value of such rare creatures, Yost quickly arranges to meet with Mr. Napoleon Lazar, a high-ranking corporate executive deeply involved in the trade of oddities. In her urgency, Yost instructs her unremarkable receptionist, Elvina Shaw, to set up a meeting with Lazar, but instead, Elvina contacts Dr. Emilio Lorca—another collector of strange specimens—who eagerly offers extra money for an exclusive "first look" at her latest acquisitions. Recognizing a possible betrayal, Lorca confers with his assistant, Sheila, and together, they hatch a plan to sabotage Yost and Lazar.
Yost eventually meets Lazar in the cold storage basement of IMSI, where she pays him to acquire the specimen. She secures a deal with Lazar, who offers her a check for $650,000 and a contract to spend at least $200,000 annually over the next decade. Meanwhile, on his way home, Lorca's scheming continues as Sheila ambushes Lazar, wearing only a miniskirt and a gorilla mask. She cuffs Lazar to a tree, steals the organism, and takes it back to Lorca's castle for examination. The scientist carefully places the creature inside a jar filled with preserving liquid, joining three other grotesque oddities that Lorca keeps stored on a shelf. These specimens are part of his extensive collection of disturbing creatures, many of which are kept in jars amidst countless other grotesque forms.
While Lorca naps, the newest specimen mysteriously reanimates the other three, revealing its horrifying form: an enlarged human-like head with two pairs of eyes and two mouths stacked vertically, a short torso, and several writhing tentacles. The other creatures include a large, blob-like entity with a face sunken into folds, a muscular, hairless ape-like creature, and a gaunt, skeletal being covered with porcupine-like spines on its head. As strange events unfold, Lazar, Yost, and Elvina seek the help of PI Leonard Kantor to track down the thief of their specimens. After some persistence, Elvina admits she informed Lorca of the sale, prompting a visit to Lorca's castle.
Lorca, eager to impress Lazar, challenges him by displaying his collection, but when they reach Lorca's private study, they find the jars shattered and the specimens missing, leaving behind footprints leading into a ventilation shaft. Lorca quickly locks down his castle with a high-tech security system, while Sheila holds the four reanimated creatures at gunpoint. The captured specimens begin to communicate through tapping on the walls, allowing the humans to decide whether to trust them. Their eventual reveal shocks everyone—the four creatures managed to escape or be released.
In the chaos, Yost trips over the skeletal creature, which becomes entangled with her and injures her with its spines. The hairless ape attacks Sheila, and the blob creature seizes the opportunity to shoot at the humans with the stolen gun. The survivors find temporary refuge in a bedroom, but the situation worsens when Elvina, frightened and injured, is attacked by the hairless ape under her blanket. She screams, flees in panic, and tragically falls over a balcony railing to her death.
The remaining characters—Lorca, Lazar, Yost (who gets caught up with the skeletal monster), and Sheila—continue their desperate search for the creatures below the castle. Lorca and Lazar attempt to lure the monsters, but they scatter into the shadows. The two men then face off in a tense sword fight, which ends abruptly when Lorca tries to escape, triggering a trapdoor filled with acid. Both men fall into the corrosive liquid as the creatures wreak havoc, with the hairless ape activating the trap.
Sheila decisively uses her security override keycard to herd the creatures onto a carpet, then sweeps them into an open acid bath, ending the immediate threat. She and Kantor drive away in his car, believing they have escaped the nightmare. However, the story hints that not everything is over—foreshadowing the possibility that the creatures might still be alive, as bloody tracks leading out of the trap remain unseen at the end, and the creatures are observed through the trunk’s keyhole. The film closes on an unsettling note, leaving the audience to ponder whether the grotesque horrors are truly gone or just waiting for their next chance to emerge.
