The Opal Deception: Artemis Fowl, Book 4

Artemis Fowl's memories of the fairy race have been wiped, and his one fairy ally, Captain Holly Short, is on the run. He needs his memory back--and fast--because a power-crazed pixie is out for revenge, scheming to overthrow the Lower Elements Police. With Holly gone, Artemis is depending on a flatulent dwarf. Things are about to explode. . .