Unwillingly keeping a journal at the behest of her brother, a monk, Birdy (daughter of a 13th-century knight) makes a terse first entry -- ""I am bit by fleas and plagued by family. That is all there is to say""-but is soon confiding her pranks and troubles in fascinating detail. Her marriage must suit her drunken father's financial needs, and though the 14-year-old scares off several suitors (she pretends to be mad, sets fire to the privy one is using, etc.), in the end she's ""betrothed and betrayed."" Meanwhile, she observes Edward I's England with keen curiosity and an open mind, paints a mural in her chamber, evades womanly tasks whenever possible, reports that -- ladylike or no -- ""I always have strong feelings and they are quite painful until I let them out,"" and chooses her own special profanity, ""God's thumbs."" At year's end she makes peace with her family and acquires, beyond hope, a possibly compatible betrothed (they have yet to meet). Birdy's frequent saint's day entries begin with pithy summaries of the saints' claims to fame; their dire deaths have a uniquely medieval tang, as do such oddities as St. Bridget turning bathwater into beer. Much else here is casually earthy -- offstage bedding among villagers, home remedies, pissing out a fire -- while death is commonplace. The period has rarely been presented for young people with such authenticity; the exotic details will intrigue readers while they relate more closely to Birdy's yen for independence and her sensibilities toward the downtrodden. Her tenacity and ebullient naÃ¯vetÃ‰ are extraordinary; at once comic and thought-provoking, this first novel is a delight. Historical note.