Book excerpt: At a time when interest in the Christmas holiday was waning, Charles Dickens wrote A Christmas Carol and inspired the world. But now, history is changing, and the book is never written. When the Council for Temporal Studies asks time travelers Simon and Elizabeth Cross to "save Christmas," they think he's joking. But it's anything but a laughing matter. Simon and Elizabeth must go back to 1843 London and convince Dickens to write his endearing story, or the Christmas holiday we all know and love will cease to be--forever.