Shelf Life is delighted to present the first peek at the titles — and covers — of the final two 39 Clues adventure books. Book 9: Storm Warning, by Linda Sue Park, comes out on May 25; Book 10: Into the Gauntlet, by Margaret Peterson Haddix, hits stores on August 31. (Book 8: The Emperor’s Code goes on sale tomorrow.) The multimedia series—each volume written by different children’s book author—is phenomenally popular in the 8-12 year-old set. It centers around Amy and Dan Cahill, a brother and sister who are, at their grandmother’s behest, searching the world for the 39 clues to the Cahill family’s power. Dreamworks has nabbed the movie rights to The 39 Clues; Steven Spielberg may direct.