Artemis Fowl and the Lost Colony by Eoin Colfer

Until recently Artemis Fowl was the only human to have discovered that fairies do exist. But now a second juvenile genius wants to capture one for scientific study – and not just any old fairy. The newcomer intends to trap a demon, the most human-hating species unknown to man.

Only an ancient time spell separates the demons from mankind – and Artemis must prevent it from unravelling. If he fails, the bloodthirsty tribe will re-launch their quest to wipe humans from the planet . . .

There can only be one winner in this battle of the demons. And it may not be Artemis Fowl.