Medieval tale of serfs, free men, and minstrel; Pearl in the Egg, by Dorothy Van Woerkom. Illustrated by Joe Lasker.New York: T. Y. Crowell. $8.95.

Dorothy Van Woerkom has fashioned a quintessential medieval story -- replete with crusades and minstrels, gypsies and gentry, serfs and free men -- and she has done it in just over 100 pages, which is no small skill in itself. The straightforward plot relies on happy coincidence and on the clear motivations of simple characters. The speech patterns of the characters, remarkably, are both comprehensible to young readers and evocative of medieval times; the believability of speech makes this story accessible and worthwhile.

When their father dies, Pearl and her brother Gavin escape from a thankless life of serfdom under Sir Geoffrey. The law holds that serfs who manage to stay for a year and a day in a town are free people, and so under cover of dark the two children set out. Beset by problems, they are eventually befriended by a wandering band of performers. Matill Makejoye, a minstrel, encourages Pearl to make music, telling her that her voice is "both sweet and well-pitched." Thus she is renamed Pearl in the Egg, because, as Matill says, "For all her life the music has been locked up inside her, till now. She needed only a prod in the right place to send it spilling out, like -- like the stuff of an egg when the shell is tapped."

Readers may want to continue elsewhere to learn more about the 13th century, as Van Woerkmon reveals only those historical considerations which influence the plot. One longs to have a better sense of the Crusades, for instance, to which most of the characters embark at the end of the book. But Van Woerkom's narrative voice is itself "sweet and well-pitched," and "Pearl in the Egg" makes pleasant reading.