Most of them contain secret information in the 'TOP SECRET" button thing. Most of the time you have to crack a code to find that. Also, the cards lead to clues. if you get a card combo, you may perhaps get a clue. not all 39 card combo's contain clues. you can also get the 39 clues card pack with 16 cards in it.
they are cards that you can unlock clues and replicators for.
The contest for free The 39 Clues cards expired in 2011. To get cards now, you must purchase them.
the books will only give you ten clues so the cards fill in the gaps along with the 39 clues website
a grate card code for the 39 clues is P32979TXXP
P4cmrfpmxp
this is a card that is reusable... P2W7RRJ4XP share it with ur 39 clues friends!
P3WJ46RRXPP369t2x9xpp22r4j4xpp24kgtxfxpp2mrhfjxpp29pcfnxpp2h2hjxxpp22d374xpp2hfrngrxpp2c2r4pxpp37g2nnxxpp2hfmpmxpp39ffm3pxpP3JGTT73XPP249F7TDXPp37jkkfpxp
P32d3ff9xpp2c2rd4pxpp2hfrngrxpp2hfmmpmxpp369t2x9xpp39ffm3pxpP3JGTT73XPP249F7TDXPP3F2M3NPXP
P2c2rd4pxpP22D3743XPP2HFRNGRXPp2hfmmpmxpP369T2X9XPP39FFM3PXPP3JGTT73XPP249F7TDXP
no
No
P2jjwkcjxp