Nikki Beckett could only watch as her boyfriend, Jack, sacrificed himself to save her, taking her place in the dark Tunnels of the Everneath for eternity—a debt that should've been hers. Now she is living a borrowed life, and she doesn't know what to do with the guilt. And every night, Jack appears in her dreams, lost and confused and wasting away. No matter how she tries to reach for his hand, she can never find it.

Desperate for answers, Nikki turns to Cole, the immortal bad boy who wants to make her his queen—and the one person least likely to help. But his heart has been touched by everything about Nikki, and he agrees to assist in the only way he can: by taking her to the Everneath himself.

Nikki and Cole, along with Cole's bandmate Max, descend into the Everneath, only to discover that their journey will be more difficult than they'd anticipated—and more deadly. From a Lake of Blood and Guilt to Sirens' alluring tricks to insurmountable walls of rock and flame, the trio is given every reason to give up. But Nikki vows to stop at nothing to save Jack—even if it means making an incredible sacrifice of her own.