"A promise can change a life. Even a small, casual promise extended without much thought or contemplation." So learns Sand Williams, who has returned to her childhood home in the Ozarks for a much- needed rest after years of working abroad as a journalist. She and her husband, Frank, a hydrologist who loves caves, have moved into a cabin that Sand inherited from her father on the beautiful Seven Point River. A mile upstream from Sand lives Norah Everston,...