"The Eternity Code" by Eoin Coiffer is the third book in the Artemis Fowl series. After Jon Spiro steals the C Cube, a super computer built by Artemis Fowl using fairy technology, the fairies must help Artemis retrieve it, lest Spiro learn the secrets of their existence. "The Eternity Code" is an entertaining account of the criminal ventures of a thirteen-year-old genius.

Artemis meets with Spiro to offer to keep the C Cube off the market for a year so that Spiro can sell his stock. Spiro however steals the Cube, deciding to keep the technology himself, and orders Blunt to kill Artemis and Butler. Butler is shot, but Artemis freezes him in a cryogenic mobile unit and contacts the fairies, who are already on alert because the C Cube pinged their security system. Holly heals Butler and agrees to help Artemis retrieve the Cube for fear Spiro will learn about the fairies, but after the mission, Artemis and Butler must submit to a mind wipe to purge their memories of anything related to the fairies.

In Chicago, Spiro is furious that his tech department cannot unlock the eternity code on the C Cube, so he sends Loafers and Mulch to kidnap Artemis so he can force him to unlock the Cube. Having worked with and befriended Artemis before, Mulch warns Artemis and becomes involved in the plan to retrieve the C Cube. Artemis agrees to unlock the Cube for Spiro, enlisting the aid of Holly, Mulch, and Juliet Butler in his plot to steal the Cube back. He leaves Butler behind to hide records of their fairy knowledge in hopes of retrieving it after the mind wipe. Upon arriving at the Spiro Needle, Artemis delays unlocking the C Cube until the next day, allowing Holly, Juliet and Mulch to break into the Spiro Needle using information gathered from the surveillance technology planted on Artemis.

Holly breaks into Spiro's room to copy his iris scan and borrow his thumb to unlock the vault, but when she returns the thumb, she realizes that Spiro left a double in his room. Meanwhile, as Artemis tries to retrieve the C Cube, Spiro appears, explaining that he used a double because he suspected Artemis of scheming to retrieve the Cube. He forces Artemis to unlock the eternity code, but Artemis opens the Cube to Foaly who reports to Spiro. Mesmerized by Holly, Pex and Chips suggest Spiro should use the Cube to steal projects from his main competitor, Phonetix. However, the Cube must be on site to access the closed system, so Spiro leads the group to Phonetix where Juliet dials 911. Using fairy technology and a quick wit, Artemis and his friends retrieve the C Cube, erase Artemis from the surveillance footage inside Phonetix, and set Spiro and his cohorts up to be arrested. Back in Ireland, Foaly performs a mind wipe on Artemis, Butler and Juliet, erasing their knowledge of the fairies. Luckily, Artemis gives Mulch a gold coin encrypted with a copy of his fairy data, instructing Mulch to return it to Artemis in several years so that he can restore his memories.