I am reading a book called Maximum Ride by James Patterson. I haven't been very far into the book, but I do know Max is the main character, and she has 8 other "siblings". They are family even thought they are not blood related. In the book, Angle, Max's sister, has been captured by the Gasman and from there they set on a quest to find Angel and get her back.
I haven't gotten far into the book to say what the theme of the book is,  but the central idea, that I think, will be about how they set on a quest to go and find  Angel. I think the main character of the book, Max, will hopefully fall in love with one of the people she lives with or someone that she meets. I predict that in the book Angel will be found by Max and she will help defeat the evil that took Angel away.