After the mysterious death of a toyshop owner, a doctor (Tom Atkins) and the man's daughter (Stacy Nelkin) investigate the Irish-dominated Northern California community of Santa Mira, a company town owned by the Silver Shamrock Novelty corporation. Atkins and Nelkin are typical low-rent horror movie protagonists, dim bulbs who discover an Invasion of the Body Snatchers-style conspiracy involving sharp-suited corporate robots. But guest star Dan O'Herlihy steals the film as a Celtic joke tycoon who hates the way American kids are despoiling the religious spirit of Samhain and decides to teach them a nasty lesson. His scheme, which involves a stolen Stonehenge megalith and a techno-magic spell that turns the heads of TV watchers into writhing masses of snakes and insects, is value for money, and O'Herlihy mixes enough serious malice into the charm to come across as a great screen bad guy.