Sarah Jane Smith and her firend Jamie Fitzoliver investigate a strange New Age cult. Business as usual for investigative journalists. But what is less usual is the demon-like creature the cultists worship. When the Doctor and UNIT arrive to investigate they discover a plot involving government ministers, alien narcotics, and an official cover-up. As an evil scheme develops on a remote island in the Indian Ocean, the Doctor enlists the help of the Royal Navy to investigate. But can the Doctor and his friends uncover the truth in time to avert disaster?