Unforgettable

``Unforgettable'' hardly describes this silly novel by Cooney ( Driver's Ed , reviewed above), although ``unbelievable'' may be apt. Readers first meet a ``breathtakingly beautiful'' 17-year-old girl from a small town just as she arrives in Boston. As she stands at an intersection, an odd-looking woman darts across the street, flings herself on the girl and seemingly seizes her purse. Amid the sound of gunshots, the woman is then thrown into a limousine by a man ``who moved so quickly there was no identifying him, no focusing on him.'' Thus the stage is set for this laborious melodrama--the major parts in which are overacted by a group of college drama students--featuring this girl (who pretends she has amnesia), a rich art smuggler (who names the girl ``Hope'' and pretends he is her father), a bizarre, knife-wielding daughter, (who is--literally--insanely jealous of Hope) and Mitch, a fabulously handsome T-shirt vendor (who falls hopelessly in love with Hope at first sight). The overwrought plot centers on a replica of a necklace once owned by Queen Isabella--suffice it to say there are no gems here, either. Ages 12-up. (Aug.)