Long before my mother was born, her aunts owned a store in a small village in Maine. They had a smart gray horse who pulled a shiny black buggy when they went out riding. Prince was the finest horse in town. But no one remembers who took care of that beautiful animal while the aunts were working in their store: perhaps it was a sneaky trader who tried to steal him, perhaps it was a one-legged harmonica player who taught him to dance; perhaps it was two children who once saved Prince's life. Jacqueline Briggs Martin, author of Caldecott winner Snowflake Bentley, really...