Regency England, August 1812: Sebastian St Cyr's plans to escape the heat of London for a honeymoon are shattered when the murdered body of Hero's good friend Gabrielle Tennyson is discovered drifting in a battered boat at the site of a long-vanished castle known as Camlet Moat. A beautiful young antiquary, Miss Tennyson recently provoked an uproar with her controversial identification of the island as the location of Camelot. Missing and presumed dead are also Gabrielle's two young cousins, nine-year-old George and three-year-old Alfred.

As Sebastian and Hero race to unmake a ruthless killer and unravel the puzzle of the missing children, they soon realize that both their lives are at risk, threatened by powerful men in high places--- and by a tall, dark [and possibly handsome] stranger who may hold the key to Sebastian's own parentage.

[mostly] from the cover.