One week after their eleventh birthday, the Fowl twins--scientist Myles, and Beckett, the force of nature--are left in the care of house security (NANNI) for a single night. In that time they befriend a troll who has clawed his way through the earth's crust to the surface. Unfortunately for the troll, he is being chased by a nefarious nobleman and an interrogating nun, who both need the magical creature for their own gain, as well as a fairy-in-training who has been assigned to protect him.