Set in the area around Plymouth and Cornwall in the South West of England, The Mistress of Essa tells the story of Corinne Redmond. During the day, she is headteacher of a popular primary school but in the evening, she is the newest apprentice of the Guardians of Essa, a group dedicated to controlling Werewolves. The Werewolves are the victims of a nasty trick of nature, to become Werewolves their babies must sleep in cradles fed by energy created by the Wraith. The Wraith demand a high price for this, they demand the pain and suffering of humans. The transportation of human suffering to the wraith caves is done via the lay lines. The Were having infiltrated human civilisation and 'arrange' for places of suffering, hospitals, prisons, etc. to be built near the lay lines. So the status quo is set. The local Alpha, David Drummond, is experienced and intelligent and keeps the peace and as many Werewolves and Humans alive as possible. He is also just happens to be the architect working on the extension of the school of which Corinne Redmond is the new head teacher. And then things get complicated.