Dirty Magic — Carol Hughes

After a night of particularly strange and vivid dreams, Joe is visited by a girl who seems to be all gray, from her hair to her eyes to her clothes. Wherever she steps, the world melts away, replaced by a land of mud and rain. Telling Joe he must come with her if he wants to save his younger sister, who is gravely ill, the girl leads Joe through to her gray world, which is in the midst of a twenty-year-old war. There Joe dodges bullets, fearsome motion-tracking tanks, and the secret police as he searches for his sister.