Trama

Devil worshipers plan to convert two new victims.

In the countryside of England, the Duc de Richleau a.k.a Nicholas welcomes his old friend Rex Van Ryn that has flown to meet him and Simon Aron, who is the son of an old friend of them that had passed away but charged them the task of watching the youngster. Nicholas and Rex unexpectedly visit Simon that is receiving twelve mysterious friends. Sooner Nicholas, who is proficient in black magic, learns that the guests are member of a satanic cult and Simon and his friend Tanith Carlisle will be baptized by the powerful leader Mocata to serve the devil. The two friends abduct Simon and Tanith expecting to save their souls but Mocata summons the Angel of Death and the Goat of Mendes to help him in a battle between the good and the forces of evil.—Claudio Carvalho, Rio de Janeiro, Brazil

When the Duc de Richelieu and his friend Rex Van Rin unexpectedly visit their good friend's son Simon Aron he immediately suspects that something is wrong. Aron is hosting a soirée of exactly 13 people, all supposedly astronomy enthusiasts. When Richelieu finds live chickens in a closet, he knows Simon is playing with black magic. He has come under the influence of the mysterious Mocata and rescue Simon and his friend Tanith Carlisle from their satanic baptism. Mocata is determined to have his new acolytes at his side however and unleashes the power of hell to take them back.—garykmcd

The Duc de Richeleau and his friend Rex discover their young charge Simon has fallen in with the powers of Darkness and is about to be baptized into the service of evil. The Duc is fortunately versed in such matters and finds himself locked in a duel with the deadly Mocata, disciple of the left-hand path.—Jeremy Perkins {J-26}

A biplane lands in an airfield. Out gets Rex Van Ryn (Leon Greene) who is met by Nicholas, the Duc de Richleau (Christopher Lee). As they drive, they discuss that no-one has seen Simon Aron (Patrick Mower) recently so they decide to go to his house.

At Simon's house there are a number of guests. Simon introduces Rex and the Duc to some of them, including Mocata (Charles Gray), Tanith Carlisle (Nike Arrighi) and a Countess (Gwen Ffrangcon Davies), claiming they are all members of an astronomical society. Simon and Mocata appear a little nervous and ask Rex and the Duc to leave as their society meeting is about to begin. The Duc is suspicious, even though the guests appear to be talking about astronomy, so says he is going to take a look through Simon's telescope. In the observatory there are some strange symbols on the wall and floor. A sound leads the Duc to find some chickens in a basket. The Duc accuses Simon of meddling in black magic, a subject which the Duc has studied, but Simon denies it. The Duc tries to convince Simon to stop but when he refuses the Duc knocks him out, carries him outside and the Duc and Rex take him to the Duc's house.

The Duc hypnotises Simon in an attempt to clear his mind, places a crucifix around his neck and sends him to bed. In bed Simon struggles to breathe with the crucifix around his neck and calls the servant. The servant removes the crucifix and Simon escapes out of the window.

The Duc and Rex return to Simon's house and enter via an open window. The house appears empty so they go up to the observatory. The Duc explains to Rex that it would be useful to know the real names of the society guests since they have to take names from other occult members. Rex says he has seen Tanith before at a hotel. They continue their search of the observatory but then the lights go out, the room becomes colder, and gas starts emanating from the symbol on the floor. A man appears from within the gas. The Duc tells Rex not to look at his eyes but Rex can't stop and starts approaching the figure. The Duc takes a crucifix from his pocket and throws it at the figure causing him to disappear and breaking the spell.

As they drive away, the Duc explains to Rex that Simon must be under the influence of Mocata and will soon be baptised into the occult and they need to find Tanith. The Duc discovers which London hotel Tanith is staying in and dispatches Rex to pick her up. As they drive along Rex talks to Tanith about Mocata, but she doesn't yield much information other than Tanith is her real name so Rex knows she hasn't been baptised yet. As Rex talks, Tanith sees Mocata's eyes in the car mirror as he communicates with her.

Rex takes Tanith to the house of Marie and Richard Eaton (Sarah Lawson and Paul Eddington) and their daughter Peggy (Rosalyn Landor). As Rex gets out of the car, Tanith jumps into the driver's seat and drives away quickly. Rex borrows Richard's car and chases after her.

A high speed chase ensues. Mocata's eyes appear in Tanith's mirror again and he tells her not to be afraid as Rex will never catch her. Rex's windscreen suddenly turns opaque causing him to skid but he punches a hole through it and recovers quickly. As Rex follows Tanith along a woodland track, a fog suddenly appears causing him to crash.

Rex returns to the road but is nearly knocked over by another car driven by the Countess. He runs after it and sees it pull into the drive in front of a large house. As he watches, several people including Simon, Mocata and Tanith come out of the house, get into their cars and leave. Rex hides in the boot of one car. The cars drive into the woods and stop. Rex follows and sees a large clearing full of occult members. Mocata starts the baptism ceremony which includes the slaughter of a goat.

Rex leaves and calls the Duc and he comes quickly to meet him. They head to observe the ceremony in the woods, during which a goat-headed figure appears sitting on a rock whom The Duc says is the Devil himself. As Simon steps forward for his baptism the Duc says they need light so he and Rex run back to get one of the cars. Driving into the ceremony with the car lights on Rex throws a crucifix at the goat-headed figure causing it to disappear. In the ensuing chaos, the Duc and Rex rescue Simon and Tanith and drive away with them. They all go back to the Eaton's house.

Tanith rests and talks to Rex while the Duc and Simon explain the situation to Marie and Richard Eaton. The Duc instructs Richard to not leave Simon for an instant because of Mocata's influence over him. As the Duc drives away, Mocata, who has been waiting for him to go, drives up to the Eaton's house and asks to see them.

Mocata introduces himself to Marie and says he is returning the Duc's car. Mocata tries to convince Marie that Simon and Tanith should leave with him but when she resists he uses the power of his mind to overcome her will and take control of her actions. Marie reveals that Tanith and Simon are both upstairs being watched by Rex and Richard respectively. Mocata uses his power to make Tanith get up while Rex is sleeping, pick up an ornamental dagger hanging on the wall and approach Rex. Meanwhile Simon is restless in his bed. When Richard approaches him, Simon starts to strangle him. Just then Peggy enters the room where Marie and Mocata are, breaking the hold Mocata is holding over the others. Mocata leaves but warns Marie that something will come that night for Simon and Tanith.

Tanith runs away from the house. Rex chases her and catches her. She tells Rex that Mocata was at the house and she tried to kill Rex. He says he will take her somewhere safe.

Later the Duc returns and Marie tells him what had happened. He is angry that Tanith and Rex have gone but Marie explains that Mocata is using his power on Tanith and Rex is trying to save her.

Rex has tied and gagged Tanith in a stable in an attempt to save her from Mocata, but Mocata through Tanith overcomes Rex's will. He unties her and she knocks him out.

At the Eaton's house, the Duc has marked a large circle with lettering on the floor surrounded by candles in preparation for the night. The Duc, Simon, Richard, and Marie lie inside the circle. The lights dim, the candles blow out, but the Duc get them all to stand back to back until the moment has passed. There is a knocking at the door and Rex's voice asking to be let in but the Duc persuades the others it is not Rex outside. A giant spider appears on the floor but cannot enter the circle. Peggy enters the room and the spider goes to attack her much to the horror of the Richard and Marie but the Duc tells them it is not Peggy. They throw holy water on the apparitions of Peggy and the spider to destroy them. Simon struggles to stay in the circle so the Duc knocks him out. They hear the sound of a horse and the Duc says the angel of death is approaching. A black horse and a skeletal rider burst into the room but the Duc repels them with the words of the Susama Ritual. In the morning when their ordeal is over Rex returns with the body of Tanith in his arms. The Duc explains the angel of death cannot return empty handed. Peggy is missing from her bed, taken in the night. Simon jumps into a car and drives away at high speed.

The Duc summons the spirit of Tanith using Marie's body to speak to them. The Duc asks the spirit of Tanith to help them. He repeatedly commands her to tell him where Mocata is but she keeps saying she can't see him because he is surrounded by darkness and guarded by a winged serpent. Rex shouts, breaking the spell, but reveals it must be the same house he had observed the occult society leaving earlier because of the winged serpent statue at the gate.

Simon enters the house. Inside are Mocata and the occult members. He asks for Peggy to be released but Mocata refuses because he has a use for her. Simon grabs a sacrificial dagger but Mocata uses the power of his mind to stop Simon. Peggy is brought in and placed on a sacrificial altar. The Duc, Rex, Marie and Richard arrive at the house as the ceremony starts. Rex runs in to stop the ceremony but is overpowered and knocked out. Mocata says Peggy's soul is going to be exchanged with the soul of Tanith. The Duc is powerless to stop Mocata as he proceeds because he has already recited the Susama Ritual to defeat the angel of death. As Mocata is about to sacrifice Peggy, Tanith's voice speaks through Marie once again. The occult members all back away as Marie/Tanith approaches Peggy and gets her to recite the Susama Ritual. As she finishes, a flash of lightning destroys the altar and sets fire to the decor in the room. The occult members and all signs of them disappear.

The Duc, Simon, Richard and Marie all wake up inside the circle back at the Eaton's house. Tanith's body is no longer there. Richard and Marie run to check on Peggy who is fine. Rex and Tanith walk out of the woods and into the house alive and well. The Duc explains time has been reversed and the angel of death has taken Mocata in exchange for Tanith since he cannot return empty handed.