(There are Spoilers) Having been into the Black Arts all his adult life London antiques dealer Neal Mottram, Jack Palance, secretly has monthly, when there's a full moon, jam sessions with his coven of witches. These sessions are held in the basement of his antiques shop to bring him as well as his followers financial rewards in what ever business that their in.
Worshiping this African Idol named Chuku Mottram has to provide it with monthly human sacrifices to keep his luck going. That resulted in him getting out of debt and becoming independently wealthy with his shop used as a front for his murderous activities.
The local police are a bit suspicious of Mottram since he's suspected of being involved in two different murders of women who were known to him and ended up savagely mutilated, and in one case burned to a crisps, and found floating in the Thames River. With Chuku constantly needing new blood to be spilled to satisfy his gluttonous appetite Mottran comes up with a plan to do in his old and rich Aunt Louise, Edith Evens. Mottron orchestrates a night out and sleep in with an old flame of his the chubby and chunky Dolly Newman, Diana Dors, who runs a Bed & Breakfast in town and whom he hasn't seen in over three years.
Getting Dolly good and drunk on her favorite brew, Cherry Brandy,Mottran checks out of her place and travels 70 miles to Aunt Louies home. Hiding in the closet Mottran catches her by surprise wearing a Halloween mask scaring the sick old lady to death. For some strange reason Mottran later drives a wooden stake through the dead lady's heart, like she were a vampire, and then drives back to Dolly's. Mottran jumps into bed with her just as she wakes up, from the effects of all the booze she drank, making Dolly think that he spent the entire evening, and a good part of the morning, with her.
The police lead by this tough talking and no BS guy Det. Sgt. Wall,Michael Jayston, feel that it was Mottram who murdered Aunt Louise? How could that be! Didn't the coroner determine that Aunt Louise was already dead before the stake, the so-called murder weapon was used to sacrifice, not kill, her by the insane Mottram? With her death being the result of Mottran scaring her to death a fact that the police were totally unaware off!
The weak link in Mottram's chain of murders turned out to be his live-in protégée in his antique shop the naive and alcoholic prone Ronnie, Martin Potter. Ronnie when he finds out about his boss' dirty deeds comes apart and starts to hit the bar scene drinking himself almost to the point of passing out. At the the same time Ronnie gets up enough courage to smash to pieces Mottram's evil idol Chuku.
Being tailed by the police Ronnie leads them to Mottram's basement where Chuku is and where Mottram just came back after he offered another blood-sacrifice to Chuku, hooker masseuses and part-time dominatrix Sally,Suzy Kendall.
Wild final with Mottram going completely berserk as he tries to defend his Idol Chuku from Ronnie's drunken ax attacks. Beating him up and throwing Ronnie head-first through the store window with the police, headed by the rough and ready Det. Wall,coming on the scene to put the cuffs on the now crazed and hysterical Mottram. Mottram didn't go, or give up, willingly and it had to take a full load of lead from Det. Wall's revolver to finally put the homicidal madman down.
