From a succession of quietly, finely perceived moments, a little boy becomes. Mossy Trotter is eight (almost and after) but his understanding of his own temptations and terrors, of the foibles and frustrations of his elders, leads to instances of mutual recognition that have nothing to do with categorical age. There's Mossy's impending birthday party, which gives him the power to select or reject among his classmates; then he ignores his mother's threat (keep out of the soft tar or no party) and she is obliged, quite reluctantly, to back it up. Mossy adjusts by assuming indifference (parties are for girls, he is too old for such silliness) but she suffers, as much for herself as for Mossy. (""This is the trouble with punishments. They spread and spread."") The situation turned around, she entices him with bigger and better balloons, pleads the disappointment of the other children, and at last Mossy gives in. Then there's the time Mossy, stuffed with sweets after an excursion with Grandfather, forces down his dinner to save Grandfather from disgrace, and two terrors that don't turn out so badly, do turn up new friends--a tonsillectomy and a wedding. The plot is simply a period of time with its normal incidents and anticipations, somewhat in the manner of one of the Moffats, and Mossy is younger than most of his indicated audience; but Rufus (M.) has his adherents, and this bead on boyhood, the first Juvenile by an accomplished British novelist, also has a potential to please.