A bio-engineered creature called a Syngenor (SYNthesized GENetic ORganism) hides in Los Angeles's sewer system, emerging at night to hunt for human spinal fluid. The brutal acts leave the police bewildered, as eyewitnesses are scarce and fingerprints are nowhere to be found, and the media mocks the investigation. The cases appear linked only by the killer’s remarkable physical feats—ripping open car doors and wrenching a victim’s hair until it snaps a neck.
Ted Londergan, John Stinson, a former detective turned novelist, is pressured by his old partner, Detective Lou Capell, Jonathan David Moses, to weigh in on the case, but he keeps dodging their requests. He’s more drawn to pursuing a relationship with Jennifer Stanton, Diana Davidson, whom he met when he accidentally backed into her car. Jennifer is initially wary of his brash, eccentric personality, yet her curiosity and his stubborn charm win her over, and they share a spontaneous kiss on their first date.
When Jennifer is attacked and left in a coma, Ted’s indifference starts to shift. A young woman named Sherry Carpenter, Toni Jannotta, steps forward with a crucial lead: Jennifer’s spinal fluid may have been drained by a Syngenor that originated in a laboratory where she once worked. The project’s lone creator, Dr. Amberdine, left behind notes warning that the creature could become dangerous if it reached maturity. Sherry’s account suggests the Syngenor’s attacks often resemble brain tumors, implying that the death toll has been seriously under-reported. The police chief, Walker Edmiston, prematurely closes the case, identifying a man killed in a shootout as the killer to spare the town from further scandal.
Ted and Sherry press on, visiting the laboratory to retrieve Amberdine’s notes. They encounter a half-dead sewer maintenance worker and realize that the sewer network is the Syngenor’s hidden transit system. Following this clue, they descend into the filthy, lamp-lit tunnels and stumble upon the creature’s lair. There, they discover a grim captive tableau: several unconscious humans connected to embryonic Syngenors by feeding tubes—the original creature has replicated asexually to produce its progeny. Ted fires at the embryos, then the adult Syngenor appears, its body seemingly bulletproof. A desperate chase ends in a metal workshop, where all exits are sealed. Ted lures the monster onto a drop forge, but the creature lands a crushing blow and strains to drain Ted’s spinal fluid. Lou bursts in, shooting the Syngenor and knocking it back onto the forge. Sherry then activates the machine, and the forge crushes the creature, finally ending the threat.
Jennifer awakens from her coma, but she emerges a changed woman, tormented by hysteria and frightening visions that linger long after the terror is over. The city breathes a cautious relief, though the memory of the Syngenor’s rampage leaves a lasting mark on those who survived the nightmare.
