
Mrs O'Neill aka Madame Rosalie la Grange

Helen "Nell" O'Neill

Inspector Marney

Helen Trent

Dick Crosby

John Wales

Lady Alicia Crosby

Major Lionel Trent

Governor Sir Roscoe Crosby

Mary Eastwood

Dr Mason

Stanby

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.

Leo, a former convict, is living in seclusion on an island with his step-daughter, the daughter of his late wife. Leo was framed by a group of former business associates, and he also suspects that one of them killed his wife. He has invited the group to his island, tempting them by hinting about a hidden fortune, and he has installed a number of traps and secret passages in his home. He is aided in his efforts by a former cell-mate who holds a grudge against the same persons. When everyone arrives, the atmosphere of mutual suspicion and the thick fog that covers the island promise a tense and hazardous weekend for everyone.