The book begins some months after The Opal Deception, in Barcelona; Spain, where fourteen-year-old Artemis Fowl Junior and his bodyguard, Butler wait for and eventually encounter a demon.Artemis is taken into the past and meets Guadi .He returns because was wearing a silver bracelet sent by Juliet "to ward off evil spirits" . Meanwhile, Wing Commander Vinyáya brings Holly Short and Mulch Diggums to secret organization Section Eight which monitors demon activity. There, Foaly informs them that the young genius was able to predict a demon materialization, something they could not do. Holly is sent to ask Artemis how he could do so.
On the demon island of Hybras, which is suspended in "Limbo" (where time is nonexistent), N˚1, an imp, is bullied because he has not "warped" (changed into a mature demon). After turning a wooden skewer into stone, N˚1 wonders if he is a warlock, though they all supposedly died. Leon Abbot, the leader of the demon pride, uses something suspiciously like mesmer to urge N˚1 to leave for the human world.
Artemis, Butler, and Holly are at the Massimo Bellini Opera House, where Artemis has predicted a demon appearance. After seeing a girl present at Artemis' first demon encounter, Artemis concludes that she knows something about demons. She is identified as Minerva Paradizo, and leaves for her residence with Holly following. N˚1, in Minerva's home, tells her about demon culture. He also learns that the spell holding Hybras in Limbo is failing. Holly has feigned unconsciousness and is in a cell with Billy Kong (one of Minerva's henchmen). She manages to knock him out.
When Artemis distracts Minerva, Holly and N˚1 escape. Kong, who has some inaccurate knowledge of demons, demands that Minerva obtain another demon to avenge his deceased brother, for which he holds demons accountable. She is unable to comply, and he takes her hostage. Artemis strikes a deal in which he will trade N˚1 for Minerva in the Taipei 101 in Taiwan. Kong plans to strap a bomb onto N˚1 and remove the silver bullet anchoring N˚1 to this dimension. However, Artemis has already removed it, and with the help of a large silver damper in the building, Holly is able to keep N˚1 in this dimension. With the suspicion that N˚1 is a warlock, Artemis asks him to return a circle of statues bearing close resemblance to N˚1 back to life as there is a possibility that the statues were once warlocks and were magically turned to stone. Only Qwan is alive. When Kong loses consciousness, the bomb is revealed. Holly, Artemis, N˚1, and Qwan leave to dispose of the bomb, but the time tunnel sucks them onto Hybras. Artemis reasons that the bomb will provide sufficient energy for a spell to reverse the original time-spell. Qwan tells him that at least five magical beings will be necessary. Artemis had stolen magic in the time tunnel, making only four with magic (Qwan, Holly, N˚1, and himself).
On Hybras, Abbot crowns himself the demon king. He is notified that four figures have appeared on the volcano, who are Artemis, N˚1, Holly, and Qwan. They accuse him of using the mesmer, but he states that demons cannot use magic. Artemis claims that Abbot stole magic from Qwan's apprentice, Qweffor. He demonstrates the fact by creating a spark out of the magic he took from the tunnel. With this development, then there will be five magical beings present (Abbot included), enough to reverse the time spell. Abbot is dragged into the circle unconscious; however, he fails to produce enough magic to support the spell. At that moment, Qweffor, Qwan's former apprentice, makes his appearance, revealing he has been living in Abbot after the first time spell was interrupted. With Qweffor's increased magic, the party is able to return to Artemis and Holly's dimension.
When they land back in the 21st century, Artemis notices that he has switched an eye with Holly. Even though Qweffor's consciousness has once again been taken over by Abbot, N˚1 manages to expand Qweffor's consciousness enough to shut Abbot out. Unfortunately, the party is three years off into the future. Artemis now has twin brothers, Myles and Beckett Fowl, Ark Sool has been fired, and Mulch has continued the PI firm (also recruiting Doodah Day). When Artemis sees Butler, Butler reveals that Minerva has grown to be "quite a beautiful young woman" who talks about Artemis extensively.