Catarina thought they'd stopped the Hydra virus. She was wrong. After laying everything on the line to decrypt the vaccine, Cat realises that Lachlan's daemon code is in the panel of every person on the planet's surface. With it, he can reprogram humanity. She, Cole and Leoben set out to stop him, but they're on a timer. Cartaxus - the shadowy corporation that's both helped and hindered them - has a deadly end game in play. The virus is evolving, the vaccine is dying, and if Cat can't find Lachlan in three days, they'll use lethal code to wipe out every person on the planet. Their path takes them to Entropia, an underground city deep in the desert and home to the most extreme gene hackers, run by the queen of coding, Regina. Struggling with the revelations about her past, and plagued by strange visions, what Cat finds in Entropia is more than just a trail to Lachlan. Because in the vaulted chambers of Regina's kingdom, Cat is forced to question everything she knows and everyone she trusts, and discovers that the biggest threat of all may be buried in her own mind.