In this beautifully written thriller, detective Aurelio Zen is called to the Vatican to investigate the circumstances surrounding the death of Prince Ludovico Ruspanti, who plunged from the roof of St. Peter's Basilica. It's hard to say what we like best about Michael Dibdin's Aurelio Zen series: his knowing police detective, the thoroughly enjoyable Italian settings, fast-paced plot or wry commentary on contemporary society and politics.  (ITL620, $12.95)