In the small town of Jefferson Valley in upstate New York, a string of civilian disappearances unsettles the community over several weeks. One day, a man covered in blood staggers into a local bar, screams, and then collapses and dies. The town’s resident scientist, Roy Anderson, examines the scene and quickly uncovers a chilling clue: the man’s blood cells are reproducing at an impossibly rapid rate, hinting at something deeply abnormal at work.
That same day, a stranger dressed as a farmer arrives at Roy’s house and is driven off by Roy’s loyal dog, Buster. The farmer, named Egon, proves to be dangerous, beating Buster to death with a cane before dropping a mysterious antique key in the struggle. The next morning, Roy’s daughter-in-law-to-be, Jenny Anderson, discovers Buster’s body hanging outside the front door, a grim omen for a town already on edge. Don Tucker, Jenny’s fiancé, ventures into the nearby woods to search for the culprit and, in the process, finds the same enigmatic key.
As the investigation deepens, it’s revealed that Egon is part of a secret druidic faction known as the Sangroids. Their leader, Creton, has a catastrophic plan to resurrect their long-dead queen, Onhorrid, by kidnapping civilians and transporting them to a secluded farm where the Sangroids drain their blood and feed it to the queen. The goal is to restore her purity and power with the help of a yet-to-be-found host. Creton scolds Egon for losing the crucial artifact known as the Key of Menanon, a key piece in their ritual.
Don brings the key to Roy for identification, and Roy calls in a friend to determine the metal’s identity. The helper, a man named Kinski, is revealed to be a Sangroid under the alias Sontag, and he hands the key back to Creton after convincing Roy that the object is nothing more than a cheap toy. The plot thickens as Roy’s experiments reveal a chemical trick: a mixture of iodine and household ammonia can cause the dead man’s blood cells to shrink at a startling rate, a discovery that becomes crucial to stopping the Sangroids.
On a date, Don Tucker and Jenny are kidnapped by the Sangroids, who intend to use Jenny as the queen’s host. Roy learns of the kidnapping and tracks the Sangroids to a quarry, where the queen is resurrected in a grisly ceremony. In a decisive move, Roy applies the iodine–ammonia mixture to the queen, destroying her and bringing a brutal end to the Sangroid threat.
