Lerangis, Peter. 2009. The Sword Thief. New York: Scholastic.
In The Sword Thief, the 3rd installment in the 39 Clues series, Dan and Amy Cahill race to Japan and Korea in search of the next clue; and alliances will be made and broken. Told in much the same fashion as the earlier books with two exceptions - Peter Lerangis adds a hint of romance (Can Ian Kabra actually be developing a more human side?) and most importantly, a sense of direction, a hint at where the clues may ultimately lead.
And…something I missed in Maze of Bones and One False Note that my book club group brought to my attention - there are clues hidden in the page numbers of each book! Have you figured them out yet?