Barclay's sixth Gregory Crowne mystery (after 2008's To Die For
) puts a fresh spin on the classic theft, revenge and murder theme. Gregory, the former crown prince of Hirtenstein, can't say no to his grandmother, that country's ex-queen mother (who's presently working as a decorator for a well-known but unpopular Italian politician), when she asks him to leave Geneva for Rome to investigate the loss of some valuable diamonds. Viewing the trip as a chance also for a romantic getaway, Gregory invites his girlfriend, Liz Blair, to join him, in spite of his grandmother's dislike of Liz and her commoner status. When a female cousin living in the politician's villa is found dead, the police conclude death by accidental poisoning, but as Gregory and Liz delve into the lives of family, guests and staff, it becomes clear the cousin was a victim of foul play. Whodunit fans will enjoy trying to figure out the puzzle before the dramatic conclusion. (June)