I bought this book along "number four" by the same author, including "the power of 6 (or 6)" is later. This is in my opinion a book for adolescents, with the basics of the genre: the action, a love story, existential questions of teenagers. The originality of this book compared to "No. 4" is only 2 stories are told in parallel: that of 4, which is on the loose with 6 and his friend Sam, and that of another number that gradually discovers her donations and history. Despite some action scenes, half of the book drags a little in length. This however leaves read with pleasure and cinema adaptation should be more spectacular than No.4.
