The Opal Deception by Eoin Colfer

Artemis Fowl: The Opal Deception is a teen fantasy novel published in 2005, the 4th book in the Artemis Fowl series by the Irish author Eoin Colfer. Preceded by Artemis Fowl: The Eternity Code and followed by Artemis Fowl: The Lost Colony, it is centered on the brilliant pixie Opal Koboi's second try at rebellion (after her first attempt was a failure) and Artemis Fowl II and his fairy comrades' efforts to stop her.