Browne's innovative picture books are always as interesting for their ideas as for their splendidly imaginative illustrations. In this story of contemporary children in an adventure with the resonance of powerful folklore, a brother and his little sister are different in every way. She's a dreamy reader, subject to night fears; he's a rambunctious ballplayer. One day, tiring of their bickering, their mother sends them outdoors together. The boy discovers and (despite his sister's pleas) disappears into a low, dark tunnel. When he doesn't return, his sister follows--only to find a frightening forest where the trees are composed of marvelously entwined animal shapes and her brother has become a ""cold hard form."" Tears and an embrace return him to himself; as they smile and become friends, the children's names are revealed in the last two lines. The illustrations here are as full of significance as the text: the exquisitely drawn faces revealing the subtleties of character and emotion; the fairy, tale details in Rose's room; the sturdy brick wall that echoes the set of Jack's shoulders; the grim vacant lot where they find the tunnel. A book to enjoy, to share, to ponder, and to read again.