Artemis Fowl and the Lost Colony (Penguin Random House Children's UK)

Ten thousand years ago, humans and fairies fought a great battle for the magical island of Ireland. When it became clear to the fairy families that they could never win, they decided to move their civilisation underground and keep themselves hidden from the humans. All the fairy families agreed on this, except the eighth family, the demons.

The demons planned to lift their small island out of time until they had regrouped and were ready to wage war on the humans once more. However, the time spell went wrong, and the island of Hybras was catapulted into Limbo, where it has remained for ten thousand years.

Now, the tainted time spell is deteriorating and demons are being sucked back into the present space and time. The fairy Council are naturally concerned about this and are monitoring any materialisations. When the spell's deterioration accelerates, the materialisations become unpredictable. Even the fairy scientists cannot figure out where the next demon will pop up.