Artemis Fowl and the Lost Colony - Eoin Colfer

Artemis Fowl, book 5 of 8, completed series

I've waited a long time for young criminal mastermind Artemis Fowl to meet his match. Finally it happened. 

A second juvenile genius has discovered that fairies do exist and she is determined to capture on for scientific study. And not just any fairy. The newcomer intends to trap a demon, the most human hating species unknown to man.

But there are more than two players in this deadly game. Holly Short has been enlisted by Section 8, a covert division of the Lower Elements Police, to find out just what her old accomplice Artemis is up to. And there is also a mysterious assassin, Billy Kong, who will stop at nothing to get his revenge. Only an ancient time spell separates the demons from mankind and Artemis mus prevent it from unravelling. If he fails, the bloodthirsty tribe will relaunch their quest to wipe every human from the planet. Because that's what demons live to do.