Margaret and Laura Davis, two old friends of Derek and Nick's, return to San Franscisco. They perfrom seances and Margaret wants Nick and Derek to come along to one of them. It seems as if Laura is being 'taken over' by a spirit, 'Elizabeth', that is taking control of her body when she is unconscious. Rachel suggests that they need to find out more about 'Elizabeth' if they want to be able to help Laura. (thetvdb.com)