The story centers around the attempts by young Wilbur Whateley to bring about, through means of ritual magic, the return of the Old Ones who used to rule this planet before mankind came along to spoil their fun. The Old Ones were supposed to be ancient, supremely powerful, but also terriby evil beings; apparently they were alien in nature, with multiple tentacles in place of arms. Anyway, Wilbur lures a lovely young virgin college student back to his place, which on a hill out behind the house features a stone altar just begging for a sacrifice to be performed on it. Wilbur has stolen the only extant copy of the ancient tome of dark magic, the Necronomicon, and is using its nefarious secrets in his rituals. But at the last minute - spoilers everyone, spoilers! - the local college professor, town doctor, and other pitchfork-carrying townsfolk arrive to stop him. Apparently Wilbur's half-Old One (on his father's side) brother gets whacked as well.
Dean Stockwell stars as Wilbur, long before he took his turn as Al on Quantum Leap, as well as Sandra Dee as the college lovely (and they don't get much lovelier than that). Stockwell is okay as the creepy young would-be sorcerer, and Sandra Dee seems to be trying to make the most of things, but it seems as if everyone involved knew this was going to be a fairly tepid offering. Most of the budget seemed to be used up on the monster, Wilbur's brother, who was only shown onscreen for a few seconds anyway. The 1970's would soon start offering a lot more supernatural-based horror movies than this one; nearly any of them are a better use of time and money than this, sad to say.
Dean Stockwell was a bit of a veteran by the time he appeared in Dunwich. He had started acting at age seven, and had starred in the cult classic The Boy With Green Hair in 1948. He continued to work steadily, in both B-movies and prestige projects, even earning an Academy Award nomination for his role in Married to the Mob in 1988, which indirectly led to his regular role as the hologram-appearing Al on Quantum Leap a few years later. He can be seen these days on the currently-popular remake of Battlestar Galactica.
Sandra Dee was for a short time America's sweeheart. Born of Russian ancestry, Sandra was doing television commercials as a toddler, and won widespread fame as the fresh-faced young beauty in the original Gidget and A Summer Place. In 1960 she married singer Bobby Darin, giving birth to a son; but the two divorced in 1967, and unfortunately much of Sandra's adult life was spent in depression, anorexia, and alcoholism. She died in 2005.