The Power of Six is the second book in the Lorien Legacies series. Things are really starting to heat up for the the Loriens in this novel.
Just a warning. This kindle book is formatted with special features for the kindle app in the Apple market. That means it doesn't look quite right on the standard kindle. A fact that I'm very disappointed about. That is not reflected in my review recommendation though. It is something I hope Amazon will correct and then re-release the book for the standard kindle hardware.
Number 4, Number 6, Sam, and BK all manged to get out of Paradise alive. Staying that way is getting difficult. In a separate thread Number 7 surfaces in Spain and she has a whole different set of problems to deal with. The Magadorians are building up forces to defeat the Loriens who've banded together. More action and adventure than the first book in the series. Very highly recommended.