C.S. Harris - When Gods Die (A Sebastian St. Cyr Mystery, Book 2)

The young wife of an aging marquis is found murdered in the arms of the Prince Regent. Around her neck lies a necklace said to have been worn by Druid priestesses-that is, until it was lost at sea with its last owner, Sebastian St. Cyr's mother. Now Sebastian is lured into a dangerous investigation of the marchioness's death-and his mother's uncertain fate.

As he edges closer to the truth-and one murder follows another-he confronts a conspiracy that imperils those nearest him and threatens to bring down the monarchy.