Silver Ashcroft, a witch who practices gray magic to protect innocents in San Francisco, encounters Hawk, a Tuatha D'Dannon warrior, after he followed Fomorii demons into the area that surrounds Silver's coven, and after the two join forces, Silver's soul becomes threatened and Hawk, who falls in love, is the only one who can save her.
Severity reflects intensity, not value — “central theme” means a warning is a core part of the book, not that the book is bad.