A handful of new fiction and nonfiction titles are percolating right below the top 15. New novels building sales steam include Missing Pieces by Joy Fielding (Doubleday), Birds of Prey by Wilbur Smith (St. Martin's) and Fatal Terrain by Dale Brown (Putnam). In nonfiction, titles moving up the charts at independents and chains are Day After Roswell by Philip J. Corso (Pocket Books) and Billions and Billions by Carl Sagan (Random House).