39 Clues books - do we have to do the online game and how does it work?

[RememberYoureAWomble]

I'm reading the 39 Clues books with 8yo DS at the moment and we're really enjoying them. But we've been getting them from the library, so don't have any of the cards.

Now I'm wondering, are we going to have a big disappointment when we get to the end of book 11 because Amy and Dan will only have found the first 11 clues and we'll have to go online to find the other 28? Do the books finish the story nicely without having to do the online game?

Also, if we want to do the online game, what would I have to buy? All the books and the clue packs or just the clue packs?

Thanks very much for any help with this.

[RememberYoureAWomble]

Anybody help with this? Thanks.