About 5 years ago I fell in love with the Artemis Fowl series. They're action-packed, full of adventure, very clever, and filled with fairy-related creatures that are interesting without being corny to the kids. Great books. They're all in the 4th-5th grade reading range, and are especially good for reluctant boys.
Artemis Fowl is a young man whose family was once neck-deep in fraud, criminal mischief, and efforts at global control. The boy is a stinking genius, and mostly uses his brainpower for greedy purposes. Along the way in the Artemis Fowl series, he changes a great deal.
The Time Paradox is the latest installment in the series. In this book, Artemis's mother is struck with a fatal illness that can only be cured by Artemis travelling back in time. While he did so, he encounters his former (bad) self, and the adventure turns into a battle of wits with himself. Just as with the other Artemis Fowl books, there are plenty of twists and turns that give you a nice surprise at the end!