A group of ruthless pirates attack a 17th Century Huguenot settlement on the Isle of Devon in search of treasure and will stop at nothing to obtain it.
American professor John Holden arrives in London for a conference on parapsychology only to discover that the colleague he was supposed to meet was killed in a freak accident the day before. It turns out that the deceased had been investigating a cult lead by Dr. Julian Karswell. Though a skeptic, Holden is suspicious of the devil-worshiping Karswell. Following a trail of mysterious manuscripts, Holden enters a world that makes him question his faith in science.
Stanley Baker's O'Donovan is sent to steal the plans of a rival company's racing car designs, to ensure his employers win the competition. However, when opening a safe containing the plans, he triggers an alarm leading to a gun battle where he kills a number of people. James Robertson Justice, alarmed by the scandal surrounding the killings, orders his agent be killed surreptitiously to hide his involvement with the plot. The film uses original footage from the Mille Miglia , an Italian open-road endurance race, featuring classic period racing cars.