Plot Summary:

Artemis Fowl and his faithful bodyguard, Butler, are visiting Barcelona, Spain to see if his calculations are correct.  His hypothesis is that a demon will appear in that area, and one does.  Its appearance is very brief, and then it teleported back a few seconds later.  Artemis then ventures to the Bellini Theatre in Catania, Southern Sicily where he finds his old friend, Holly Short.  At the Theatre, he sees a young girl, whom he later finds out to be named Minerva Paradizo.  She has two bodyguards accompanying her.  When the demon that Fowl predicted would show up appears in the back corner of the stage, the only ones to notice the small creature were Artemis, Butler, Holly, Minerva, and her two guards.  The one guard shot a silver dart into the demon's leg, knowing that once the demon was touching silver, it could no longer teleport away from the stage, and, more importantly, into another dimension.  Minerva's bodyguard grabbed the unconscious demon and brought him back to the Paradizo's mansion.  Artemis said that he would not intervene with the situation, but Holly eventually convinced him to change his mind.  Foaly, the Section Eight computer wiz, gave Holly and Artemis all of the information he had relating to Minerva and her family, so that they could fully understand who they were dealing with.  Section Eight is part of the secret underground fairy world known as Haven.  Section Eight promoted Holly Short to Captain and put her in charge of demon related missions.  No one knows about the fairies except for Artemis's party and Minerva's party.  Holly devised a plan and successfully rescued the demon warlock imp, who calls himself No1.  Soon after, Minerva's bodyguard, Billy Kong, took Minerva hostage, demanding her to capture another demon in exchange for her release.  He wanted another demon, as he had a plan to destroy all of the demons, since he mistakenly believed that the demons were responsible for his older brother's death many years ago.  Artemis convinces Kong to meet at an art gallery, where Artemis will hand over No1 to Kong if he, in return, will set Minerva free.  The two meet at the gallery where Butler is ready to take out Kong inside the front door.  Unexpectedly, Kong brings his old gang for reinforcement.  When Butler begins to fight, everything quickly spirals out of control.  As Holly tries to free Minerva, Kong accidentally handcuffs a bomb to Holly's wrist.  Kong planned for the bomb to be placed on No1's wrist, where Kong would then take out the silver dart. Then No1 would be sent back to his dimension where the bomb would explode, blowing up the entire Island of Hybras.  During the confusion, No1 uses his warlock powers to release Qwan, one of the only warlocks that was not frozen in time but frozen in stone..  No1 could only do this, since the ancient stone of the warlock was displayed in the art gallery.  Artemis instructs Holly to use her jetpack to carry Artemis, Holly, Qwan, and No1 away to another building, so he could defuse the bomb, but the jetpack breaks, as there is too much weight being carried.  Artemis quickly goes to Plan B.  He removes the silver dart from No1's leg that anchored the demon to this dimension, and it teleports the four of them to Hybras, Limbo where all of the demons live.  

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Conclusion:

In Hybras, Artemis and Qwan devised a plan where five magical beings are needed to reverse the time spell.  If they reverse the time spell, they can return Hybras to Earth.  However, Abbot, the leader of Hybras, thinks that Artemis and his friends are there to attack the demons, so the two sides go to war with each other.  Artemis, No1, Holly, and Qwan use their skills to outwit Abbot and the demons and, therefore, win the battle.  After this, Artemis puts his plan in motion and reverses the spell.  Finally the island of Hybras is saved, and the demons will no longer float through dimensions uncontrollably.  The novel ends, however, when Artemis and his gang get back to Earth and realize they have been gone for three years.