The Opal Deception (Artemis Fowl, #4)

Artemis has no memory of the fairy people and has returned to his unlawful ways. In Berlin, he is preparing to steal a famous Impressionist painting from a German bank. He doesn't know that his old rival, Opal, has escaped from prison by cloning herself. She's left her double behind in jail and, now free, is exacting her revenge on all those who put her there, including Artemis. Meanwhile in the lower elements, Captain Holly Short of the LEPrechon fairy police is framed for a heinous crime, yet she manages to elude her captors and escape to the surface to rescue Artemis. But before Holly and Artemis can get away, Opal arrives and abducts them both, forcing Artemis to go head to head with an enemy who plans on destroying the fairy world forever.