TO KEEP AN ISLAND

In her second book, Scott has transposed the basic plot of Cross Fox--a child protecting nature against a friend's father--to a New England coastal setting. But she's also traded the unhappy-loner/solace-in-nature gloom, and the quasi-mysticism, for the exhilaration of active kids vacationing at the shore. Newly arrived at the Point, Tina, a bubbly, easily miffed eleven, and her shy, bright brother Josh, nine, find Harry Bourne looking in on them. Harry is a twelve-year-old New Yorker, the only child of the Point's richest property-owner, a cynic warring with his stepmother, and not to be trusted; but he has a boat and access to the enticing little offshore island--which, he says, his father is purchasing for him. The three form a club and build a tipi on the island--Harry dominating through know-how (years of camp), sophistication (a casual cigarette), and that edgy personality. Tina picks up some of his rudeness and hostility; and the two begin to freeze Josh out. Later, when Harry thinks Tina has been faithless, he'll cozy up to Josh and freeze her out. (""Now maybe you know how I felt,"" says no-pushover Josh to Tina.) The rift is caused by Harry's maliciously stealing plants from elderly Mrs. Wetherill, ""land-poor"" doyenne of the Point, who makes him feel uneasy, inferior. (Tina, accused, clears herself without tattling.) But what's in the offing is only discreetly signaled: Harry's father really--and realistically--intends to build houses on Harry's forever-wild island. (He never said otherwise.) Tina's solution--arrived at after a low-key shipwreck, accident, and rescue episode--is a clever authorial ploy: if Harry's father will leave the island alone, Harry will ""be nice to Caroline,"" his stepmother (and generally shape up). Highly unlikely in the outcome; but a likable mix, nonetheless, of summer moods, strongly-defined characters, and up-front values.