What does the theft of Lord Henry Naismith's prize Monet--the latest of a well-oiled series of art robberies from some of England's finest homes--have to do with a lethal spate of industrial extortion over at Kerrchem, Trevor Kerr's cleaning-chemical company? Nothing, really, except that Manchester p.i. Kate Brannigan, whose firm installed Henry's security system, is on both cases. Kate has surprisingly little trouble identifying the art thief, but her chase for bigger fry will lead her from Antwerp to Genoa to a histrionic drop-dead scene with her lover, rock journalist Richard Barclay. On the Kerrchem front, she'll taste first blood again--fingering a probable blackmailer early on--but the case will grind on for ages before she's finally able to figure out why the blackmailer didn't just threaten to adulterate shipments of KerrSter with caustic soda but felt moved to spike two especially nasty bottles with cyanide. Kate, whose first three books (Crack Down, 1994, etc.) showed a fine line in wisecracking without the depth McDermid wants to claim for her here, does yeoman work on the art thefts from beginning to end. The Kerrchem quagmire, though, is a mess even when she gets done mopping up.