The measure of good sci-fi writers isn't just the worlds they create, or even the characters they place within them; it's also the extent to which they can find new stories to tell in those worlds. At last count, Orson Scott Card had spun 11 tales in his Ender-verse, which revolves around a boy genius conditioned to wage an interstellar war. Card's latest — A War of Gifts, a Christmas novella, of all things — tucks very neatly into young Ender's days at the Battle School. Full of religious fire, preternaturally mature sentiment, and far-reaching ramifications for the series, War is a perfect sci-fi stocking stuffer. A