Having finally rescued Jack from the dark Tunnels of the Underworld, all Nikki wants is to be with him and for life to return to normal. But Cole tricked Nikki as they journeyed through the labyrinth of the Everneath, and now she's started turning into an Everliving just like him. Desperate to find a way to reverse the process, Nikki and Jack try everything they can think of. Even Cole becomes an unlikely ally, but for how long? Nikki needs to feed on Cole to survive, Cole needs Nikki to gain control of the throne in the Everneath, and Jack needs Nikki because she is everything to him. Together, they must travel back to the Underworld to undo Nikki's fate and make her mortal once more. Will Nikki be forced to spend eternity in the Underworld - or does she have what it takes to bring down the Everneath once and for all?