Artemis Fowl series

When twelve-year-old evil genius Artemis Fowl tries to restore his family fortune by capturing a fairy and demanding a ransom in gold, the fairies fight back with magic, technology, and a particularly nasty troll.

After his last run-in with the fairies, Artemis Fowl's mind was wiped of memories of the world belowground and any goodness grudgingly learned is now gone with the young genius reverting to his criminal lifestyle.

Artemis's mother has contracted a deadly disease -- and the only cure lies in the brain fluid of African lemurs. Unfortunately, Artemis himself was responsible for making the lemurs extinct five years ago. Now he must enlist the aid of his fairy friends to travel back in time and save them. Not only that, but he must face his deadliest foe yet...his younger self.

Seemingly nothing in this world daunts the young criminal mastermind Artemis Fowl. In the fairy world, however, there is a small thing that has gotten under his skin on more than one occasion: Opal Koboi. In The Last Guardian, the evil pixie is wreaking havoc yet again. This time his arch rival has reanimated dead fairy warriors who were buried in the grounds of Fowl Manor. Their spirits have possessed Artemis's little brothers, making his siblings...