Colonel Bingham (Christopher Lee) is investigating the mysterious death of an old friend and two other Trustees of a Foundation which runs an orphanage in Scotland. Bingham enlists the help of pathologist Sir Mark Ashley (Peter Cushing) after disaster strikes when a bus carrying the orphaned children crashes killing the driver. A pupil, Mary (Gwyneth Strong), is hospitalised following the crash and with the help of Dr Haynes (Keith Barron) and hypnosis, discovers that the girl is suppressing memories of a traumatizing fire. Meanwhile a convicted murderer and prostitute, Anna Harb (Diana Dors) claims to be Mary's natural mother and seeks custody of the child. Mary is returned to the orphanage in Scotland but her behaviour is becoming more eccentric as Harb tries to recover he lost child. Mean-while, Bingham tries in vain to discover who is now responsible for the welfare of the children and controlling the orphanage. However he uncovers a dark and deadly plot by a satanic cult that leads to a tense and disturbing climax.