Artemis Fowl And The Opal Deception By Eoin Colfer

Artemis has had his memory wiped.

He remembers nothing about the fairy people.

Down in there city the last goblins who had played part in the goblin Revolution had been locked up. And the pixie behind it has been in a coma for a year.

But they don't know that she has woken and the pixie in her place is a clone.

Now the fairies must bring Artemis's memory back before it is to late.