In the three previous Deadly Sin cases for crusty NYPD veteran Edward X. Delaney, Sanders used violence and vulgarity--some of it from the psycho-criminal's viewpoint--to juice up uninspired police-procedural. This time, however, the doings are much tamer, much duller--as an utterly routine murder-mystery is padded out to nearly 400 pages with humdrum sleuthing and interminable talk. The murder victim? East Side psychiatrist Dr. Simon Ellerbee, hammered to death in the townhouse/office he shared with psychologist-wife Diane (a wealthy beauty). The prime suspects? Dr. E.'s six most volatile patients: a sadistic bully, a tortured Vietnam vet, a chirpy homosexual (one of several dated stereotypes), a retarded youth, a matronly agoraphobe, and a suicidally inclined spinster. So retired super-cop Delaney, with eight NYPD-ers assisting him, does close-up investigations of these six wackos--concentrating on their alibis (a knotty, contrived jumble) and their hypothetical motives for killing the shrink. (Did he force one of them to face some ugly truth, thereby triggering massive anger?) The few half-intriguing moments here involve the relationships that develop between some of the cops (two compassionate, one brutal, one nastily seductive) and some of the suspects. But finally, after Delaney realizes that the late Dr. Ellerbee had fallen in love in the months before his demise, the case takes on a new direction--one that will come as no surprise whatsoever to most readers. Ho-hum plotting, oddly unconvincing N.Y.C. backgrounds, stale dialogue abounding: the weakest psycho-puzzle by far for Iron Balls Delaney--whose mixture of cutesiness (with wife Monica) and boorishness (with everyone else) has become thoroughly unappealing.