During the six days it takes Sal's paternal grandparents to drive her west to Idaho in time for her mother's birthday, she tells them about her friend Phoebe -- a story that, the 13-year-old comes to realize, in many ways parallels her own: Each girl had a mother who left home without warning. The mystery of Phoebe's more conventional mother's disappearance and its effects on her family and eventual explanation unfold as the journey, with its own offbeat incidents, proceeds; meanwhile, in Sal's intricate narrative, the tragic events surrounding her mother's flight are also gradually revealed. After Sal fell from a tree, her mother carried her back to the house; soon after, she bore a stillborn child. Slowyly, the love between Sal's parents, her mother's inconsolable grief, and Sal's life since her departure emerge; last to surface are the painful facts that Sal has been most reluctant to face. Creech, an American who has published novels in Britain, fashions characters with humor and sensitivity, but Sal's poignant story would have been stronger without quite so many remarkable coincidences or such a tidy sum of epiphanies at the end. Still, its revelations make a fine yarn.