Though billed as ""A Norah Mulcahaney Mystery,"" O'Donnell's latest police-procedural features super-cop Norah in only a small cameo role this time. Instead, the hero here is Norah's ex-lover, Detective Greg Reissig (Lady killer), now married to a young second wife--who isn't thrilled with Reissig's workaholic devotion to his duties in Far Rockaway, Queens. In the novel's gripping, rather gothicky first half, Reissig does his best to provide protection to young music/dance teacher Alyssa Hanriot--who is near-fatally attacked by an unseen knife-wielder, then terrorized with threats, stink bombs, the obligatory murdered-cat. Who's behind this savage harassment? Well, it seems to be obvious: the culprit must be Roy Easlick, a teacher just released from prison after being convicted of molesting two little girls--largely on the basis of Alyssa's testimony. But Reissig can't get any solid evidence against Easlick. Then, when Alyssa is found shot to death, the creepy ex-con has an alibi. So, prodded by Norah, Reissig starts considering other possible motives and suspects, an unlikely array--from Alyssa's two-timing boyfriend to Easlick's insane fiancÃ‰e (a weak psycho-portrait) to others involved with that child-molestation trial. And, after Easlick himself is murdered, Reissig closes in on the wildly improbable, weirdly motivated culprit (in a melodramatic, child, as-hostage finale). Dismayingly far-fetched--and Norah fans will find Reissig an only so-so substitute--but those riveting opening chapters and O'Donnell's plainly readable narration will carry most readers straight through to the end.