When Gods Die — C.S. Harris

June 1811. The beautiful young wife of an aging marquis found dead in the arms of the Prince Regent. From her back protrudes a jeweled dagger. Around her neck lies a bluestone-and-silver necklace said to have been worn by Druid priestesses--and reputed to have mysterious powers. That is, until it was lost at sea with its last owner, the mother of Sebastian St. Cyr, Viscount Devlin.

Shadowed by rumors of his dark past, Sebastian is lured into a dangerous investigation of the marchioness's death and his own mother's uncertain fate. Aided by his actress lover and pickpocket servant, he follows a twisted trail from a seaside palace to London's most depraved slums. As Sebastian edges closer to the truth--and one murder follows another--he confronts a conspiracy that imperils those nearest to him even as it threatens to bring down the monarchy.