Scotland Yard's Merle Capricorn is in America this time--in and around the UN (the ""Rockefeller Gift""), an institution which Winslow takes time out here and there to denounce vehemently. Ostensibly Merle has come to N.Y. at the request of his Aunt Dolly, who's furious about Aunt Nelly's affair with a Swedish diplomat. (All three madcap aunts--they're magicians--are starring on Broadway.) But the real reason is professional: one young, high-living British diplomat (a spy) has died of an apparent drug-overdose; and another diplomat has disappeared (soon to be fished out of the river). Could this be because they caught on to some scheme to be perpetrated by the KGB spies at the UN? Merle investigates, concentrating on the sexy, Sohoartsy banker's wife with whom the young, dead diplomat was having an affair. (Could the motive have something to do with the banker's vast holdings of Middle East gold? A plot to rob the Federal Reserve Bank?) And Merle also falls for an elegant, cultured private-school teacher . . . while avoiding the clutches of a gorgeous young secretary (who seems to have been everybody's mistress). All in all, another slide in quality for talented but slipshod Winslow: lazily over-plotted, largely implausible, too effortfully comic (the aunts are again a bit too much), and only very sporadically charming.