The Seal by Meg Hutchinson
Journalist Kate Mallory is covering a routine case of vandalism in a local churchyard when she comes across a mysterious foreign banknote and a drawing of an ancient talisman, the Seal of Ashmedai, used in rituals of black magic. At the same time, Richard Torrey is haunted by a young woman, dressed in white, who begs his help. But why can no one else see or hear her? Together, Kate and Richard decide to investigate a possible connection between these random events. They do not expect to find themselves embroiled in an attempt to create the havoc of war in the Middle East, large-scale currency counterfeiting - and devil worship.