Burning Issy by Melvin Burgess
Nobody knows where Issy came from. Rescued from fire as a baby, she lives peacefully with kindly Nat and his son, Ghyll. But then hysteria about witchcraft startsto mount, and Issy finds herself amongst the accused. So when the powerful Iohan offers her a means of escape, she cannot refuse.
For a while Issy is happy with Iohan. Then, haunted by dreams of flames and shocked by new-found powers, she begins to doubt her own nature. After seeing Iohan and her friends frolicking with what appears to be the devil, she flees, believing that her own salvation depends on their undoing. And so she confesses to witchcraft and accuses her friends . . . only to realise too late that not all witches are evil . . .