Artemis Fowl (sorry) is a supersmart twelve year old kid with special talents.
He is the bad guy.
Elfs and gnomes and such exist, but they're not magical, they're simply incredibly technologically advanced (and biologically different from humans).
Artemis finds out about this secret world and puts into motions plans to get the faeries' gold. He gets into fights with gnome (or elf or something) secret service agents (with gadgets and all).
I've heard them described as Harry Potter meets James Bond, which kinda fits, although not as good as those.
These books are pretty funny, but not to be taken seriously. A quick read.