``Thou shalt not overlap'' is the unofficial commandment of the CID, but Chief Superintendent Colin Harpur (Astride a Grave, 1996, etc.), continuing to flout the rules, has fallen out of lust with Assistant Chief Constable Desmond Iles's wife Sarah only to take up with Denise Prior, a first-year university student whose friend Helen Surtees is the live-in companion to Jack Lamb, Harpur's most venerable informant. A dangerous situation for sweet Denise--especially since crime-family patriarch Doug Webb strongly (and accurately) suspects Lamb of dealing Harpur the information that let the coppers get the drop on Doug's son Martin, witless mastermind of a third-rate robbery that left Martin dead and his father grimly bent on revenge against everyone who might've been involved. Scrambling to keep Denise out of harm's way, Harpur still has time for a spot of breaking and entering, an accidental episode of eavesdropping on Iles's latest tryst, and several matey conversations with panicking Ralph Ember, the hopelessly middle-class thief-cum-pub- owner who can't get over his jealousy of Lamb's Gatsby-like success. Meantime, all concerned act as deviously uninterested as possible as they race toward the climax at Lamb's annual fancy- dress ball. Lamb's gospel of principles--he feeds information only where there's the risk of violence to bystanders, or where he has a personal grudge against the planners--is the perfect focus for this ninth installment in James's heartlessly funny series.