The Fern Capel series: Prospero's Children, 1999; The Dragon Charmer, 2000; The Witch's Honour, 2002
In the first of the three books, Prospero's Children, Fern Capel and her brother Will accompany their father to Yorkshire to look at a house that has been left to them by an elderly cousin. Although Fern, who has been "managing" her father since her mother's death, regards the house as too cold and impractical to keep, it nonetheless exercises an odd compulsion which makes them return, this time with their father's girlfriend, Alison, whom Fern deems unsuitable for her father. It soon becomes clear that Alison is there for her own ends; not only a witch, she is also under the sway of an Old Spirit, Azmordis, who speaks to her through a stone statue in the house, and she is using the Gift - her magical powers - to search for the key to the Gate of Death, which she means to open. In so doing she inadvertently opens the door to the lost land of Atlantis, dying in the process. Only Fern now has the Gift and can go to Atlantis to find the key and close the door.