Ruth Rendell or Patricia Highsmith might have made something neatly scary out of the small-scale premise here: a woman's murderous rage against her husband's sadistic ex-wife, queen of the crippling alimony demands. But, alas, as readers of the crude The Thursday Woman or the unspeakable Hot Spot well know, Davidson is no Rendell; and this high-strung melodrama is padded out with the sleazy doings of unpleasant people. Davidson's heroine is Kate Griffin, fashion director of an L.A. department store and wife of established photographer Paul. But Kate and Paul's combined income is no match for their financial pressures: Kate's sister, in a quasi-coma ever since an alcoholic accident, needs expensive nursing-home care; and Paul's frigid, crazy, narcissistic ex-wife Nancy in N.Y., though rich herself, gets one-third of all his earnings--thanks to some unbreakable contracts that Paul signed to get out of the marriage. All this is laboriously explained in flashbacks . . . while the Paul/Kate marriage is fraying: a drunken Paul even attempts adultery with Kate's promiscuous pal, model Natalie. So, when Kate and Natalie go to N.Y. on business and oh-so-coincidentally wind up staying right next door to ex-wife Nancy, Kate's thoughts naturally turn to homicide. Unfortunately, however, instead of focusing in on this potential suspense, Davidson throws in a mess of subplots: Natalie is promptly attacked in Central Park, her ears damaged by an earring-snatcher; Kate graphically discovers the joys of promiscuity with Natalie's plastic surgeon (whose Jewish mother appears briefly, saying ""I swear you'd forget your scrotum if it weren't attached to your cock""); and, most extraneously of all, Natalie tells Kate her big secret--that she's the granddaughter of famed traitor Quisling. Finally, though, Kate does (in a wig disguise) worm her way into unhinged Nancy's confidence--and there are some contorted last-minute twists about how Nancy gets hers. True, Davidson works hard at heaping up the Griffins' woes, casting Nancy as a deserving murder-victim, but Kate--alternately a whiny marshmallow and a noisy pain--will get few readers' sympathy. And Davidson's relentless, wearying vulgarity combines with the ragged plotting to make this second-rate psychosexual suspense, even if slightly more plausible than Davidson's others.