First off, this third installment in the Halloween series is not an installment at all, in fact, Season of the Witch has nothing at all to do with the world of Michael Meyer, save the fact that "Halloween" is playing on the television every now and again.
Another oddity is the title, Season of the Witch, since there are, in fact, no witches at all in the film. Sure the main villain fancies himself a warlock, but that's not a witch.
The acting's shoddy, the direction is shaky, and the score isn't as spooky as the other Halloween's, but despite all this, Season of the Witch manages to create an unsettling atmosphere, and, by the finale, a tense feeling of impending doom.
The basic plot begins with an old man being terrorized by some fancy suited men. Clutching a Halloween mask, he finds his way to the hospital where he's treated by Dr. Chaliss. That night another suited man enters the hospital and kills the old guy, then goes and blows himself up in his car. The old guy's daughter, Ellie, comes to see him, and then decides to investigate his murder. Dr. Chaliss, a lonely, surly divorcee, decides to accompany her. And in a totally unrelated matter, they do it.
Their only lead is the mask Ellie's pop was clutching so tightly, so they go to the town where the mask's factory is located. There they find out much more than they needed to know, including the mystery behind the factory, and it's owner, who want's to bring about his own witchcraft armageddon via the television.
Sure it's hokey as all hell, but it's fun and entertaining, and isn't that what we really want in a movie?