Okay this is an awesome series that are supposed to have 10 books, the last one coming out September 2010. Which is more than a year from now. The series is written by five authors altogether (one per book) Rick Riordan (Percy Jackson & the Olympians author) Gordan Korman, Jude Watson and Patrick Carman. So far there are three books out (Maze of Bones, A False Note and The Sword Thief)and a fourth coming out in June (Beyond the Grave which is set in Egypt by the way)
POSSIBLE SPOILER: The Cahill family consists of pretty much every famous and historical person you can think of and more (if AH was in it he'd be either a Lucian, Ekat or Janus

) and there is four branches-Ekaterina (founded by Katherine) Lucians (Luke), Tomas (Thomas) and Janus(Jane). Each branch has its specialty Ekat-smartie, Lucian-spy,strategic things, Tomas-things like sports, world records and Janus-performing arts. So the father of the four siblings was doing a project that could change mankind. An alchemic wonder. He found out 39 ingredients (the clues) that could create the (gasp) Philosopher's Stone. So now Grace Cahill selected forty people before she died (this takes place during the reading of the will) to go search for the clues or take a million dollars. Only few took the hunt. It basically revolves around one team, Amy and Dan Cahill.Also for us readers WE can be part of the clue hunt (and we dont have to travel around the world)there is a code in the page numbers of the books and also sometimes in the cards there are codes.You can add the cards to your collection in the 39 clues websiteTHIS SPOILER ENDS.
ULTIMATE SPOILER THAT I FOUND OUT:Okay i have a account on the site and including the ones that came with the books, Ive got 6 clues (Im trying to uncover a 7th) and they are: Iron Solute, Tungsten, Fire, Gold, Uranium and King Cobra Venom. And Ive managed to decode one of the codes in the page numbers (the one in book 1) It says: Anne Cahill, die not drown. For those who has started Mission 2 in the site will understand...
Anyway its great books and its fun too...