Robert Barnard, writing his second novel as Bernard Bastable (To Die Like a Gentleman, 1993), has fun with the story of a 64- year-old Wolfgang Gottlieb Mozart. The impecunious, self-pitying composer of Don Giovanni and Le Nozze di Figaro, living in England from boyhood, yearns still for all things German and feels ill-used by the English--especially by aristocrats like Lord Hertford, who supports the Opera House, and by impresario Mr. Popper (a musical ignoramus in Mozart's eyes), who runs it. The year is 1820; the Prince of Wales is about to ascend the throne. Caroline of Brunswick, his drunken, amoral wife, though supported by the rabble, is on trial before the House of Lords as unfit to share the crown. Meanwhile, Jenny Bowles, a snivelling housemaid at Caroline's temporary residence, brings Lord Hertford a particularly nasty report on her behavior. Jenny is given a job as dresser to singer Betty Ackroyd until her testimony can be heard--but before that happens she's found stabbed to death backstage, with Mozart a complaisant if uneasy participant in the disposal of the body. It's Mozart, though, who inadvertently stumbles on the killer and contrives a devious justice. The mystery here is rather feeble window dressing for a wittily ironic study of genius beset--and of the life and times of royals who make today's seem a bunch of innocents. For music mavens, a tour de force; others may wish for more Barnard, less Bastable.