 Silver Shamrock, a mass-producer of Halloween masks, plan to kill millions of innocent people worldwide by placing pieces of a stolen boulder from Stonehenge into small tags and attaching them to the masks. When children all over the world sit down to watch the Silver Shamrock advertisement, terror and panic will spread. Dr. Dan Challis investigates a series of bizarre and horrifying incidents that begin to unfold before Halloween evening, and he comes face to face with the sinister figure of Conal Conhran, maker of the evil masks.