Blond twins run in the family
It's the code on the bottom of every card in the clue hunnt cahill vs vesper card only have 1 per book or 1 per card pack
The only card that has a reusable code is the Surveillance Camera card (card #1) that comes with The 39 Clues Book 1: The Maze of Bones.
Other codes can only be used once. If the card code has already been entered in your gallery or another player's gallery, it won't work for your gallery.
it doesnt have a code. no one in the world has ever cracked it. not even the authors
you enter in the reusable code:P2JJWKCJXP
Once you have collected all the cards for a certin book, you unlock the question for the book. Once you complete the book question, you get a replicator.
a=1, b=2, c=3, etc... So, the answer is: never forget what you lost