Borowitz, author of dullish true-crime essays (Innocence and Arsenic, 1977), proves even less adept at crime-fiction in this amateurish mystery debut--which takes place in 1988 London, during the centennial of Jack the Ripper's 1888 murder-spree. Prof. Paul Prye (Urban History, Columbia), on vacation abroad with prof-wife Alice (Art History, NYU), is a fanatical crime-history buff. So he naturally joins a walking tour of Jack-the-Ripper murder sites--during which theater-director Margaret Sanders is nearly hit by a speeding motorcycle. Did someone actually push Margaret into the motorcycle's path? So Paul believes. And when the newspaper a few days later announces her death (from natural causes, apparently), Paul is sure that she was murdered. How? By slow-acting ricin poison, of course, delivered by an umbrella-tip jab (remember the famous Markov case) during that motorcycle melee! Paul soon has his suspicions confirmed by Scotland Yard. Furthermore, it quickly becomes apparent that some psycho--determined to outdo Jack the Ripper--is planning to commit a whole string of poisoned-umbrella killings in Ripper-related settings. And Paul will eventually help the Yard to save the last intended victim (the soprano playing Lulu in the Berg opera) from the killer: a woefully implausible, murkily motivated lunatic. Despite this lurid material, however, Borowitz's thin narrative is virtually all talk--with laborious explanations, turgid theorizing, and leaden repartee between the erudite (but tiresome) Pryes. So, while a few of Borowitz's fellow true-crime buffs may enjoy the long-winded chatter about old cases here, suspense fans will find little in the way of character, action, or credible mystery.