Four young people, including the wealthy Bill, Joe, Fred, and Jane, knock on the door of a remote villa when their dune buggy runs out of gas following a tranquil sailing trip. Bill had gifted the attractive Jane a pearl necklace with a reportedly paranormal past earlier in the day, and this opens a can of worms later on. They are invited to spend the night in the mansion owned by Lord and Lady Alexander, who are hosting a ceremony attended by a group of eccentrics dressed in black robes. Jane emerges from her sleeping chamber in the evening, seemingly in a trance, and is lured to a sacrifice altar where robed houseguests hover over her. As a knife is about to be plunged into the young woman, three of her friends rush to her aid, but they also witness a frenzied mass murder and run with emotions of guilt and doubt.