The harlequin - Laurell K. Hamilton

The first warning is unexpected, calculated. Malcolm, head of the vampire Church of Eternal Life, is no friend to Anita Blake. So when he asks for help, against creatures so feared that no vampire will willingly speak their name, Anita is surprised. But the Harlequin require different rules. The second warning is presented like a gift, with 'Anita' printed on the box. Inside, carefully wrapped in folds of pristine tissue paper, is a plain white mask. The fact that it's white is good news. White means they are only being watched.

The power connecting Anita with Jean-Claude, vampire Master of the City and Richard, Ulfric of the werewolves, has been increasing exponentially - and this has attracted very unwelcome attention. Anita Blake has the authority to pass judgment on vampires. The Harlequin have the authority to pass judgment on her. It is forbidden to speak of the Harlequin unless you've been contacted. And to be contacted by The Harlequin is to be under sentence of death.