Reader, remember, this was a different world."" Many, many readers remember and the fact that this is a different world, a penultimately proper one in which the checkbook competes with Gotha, is one of its attractions. Auchincloss, who has been writing novels of manners and professions (mostly the law until the overwhelmingly successful Rector of Justin) and backgrounds, (again mostly New York, Tuxedo Park, Newport) for years, has again used the device which proved so successful in his last book. Variant versions of one life are given, this time only three, as the end of it is reached in Panama by Guy Prime, following certain ""irregularities"" he had committed, ""borrowing"" from trust funds including his wife's. He tells the story in which he appears as something of a blueblooded Babbitt whose margins are not much wider than his country club, his Long Island estate (a parvenue word-- all these slight distinctions are made) and his brokerage. And this is followed by that of his wife, who loved him at first, and later had an affair with his oldest friend Rex Geer (no connections, much intellect and industry) who also interprets his- her- their story. As in all of Auchincloss' books, money and background not only immunize his characters but to an extent deprive them of passion-- even on occasions when they profess it most strongly. But his novel (stronger than many he has done in the past) is a poised, proportioned entertainment which certainly his new audience, following The Rector of Justin, will underwrite. And that Standard & Poor of the industry, the Book of the Month Club, has selected it for March.