Artemis Fowl: The Opal Deception

This is an okay book written by Eoin Colfer. After his last run-in with the fairies, Artemis Fowl had his mind wiped of his memories of their world below. Any goodness he had grudgingly learned is now gone, and the young genius has reverted to his criminal lifestyle. Artemis is in Berlin preparing to steal a famously well-guarded painting from a German bank. Little does he know that his every move is being watched by his cunning old rival, Opal Koboi. The evil pixie has spent the last year in a self-induced coma, plotting her revenge on all those who foiled her attempt to destroy the LEPrecon fairy police.

This is the fourth book in the series. There is a secret code at the bottom of the book, in the Gnommish alphabet.