She's always been good in fights. But can she kill to survive?

Hunting artifacts while being hunted by deadly creatures that are impossible to outrun. That's what Sienna must do. The DEZ might have given her military training, but nothing could have prepared her for her new life in The Void. Sure, there are other Marked kids in this vast, dark place. But they're not her friends – they're competition.

At least she has Theo. But where is Vic? Sienna knows her innocent friend will never survive in a place like this. She has to find her. Even if it means killing every Reek she can find.

Meanwhile, Jayla is struggling to come to terms with the loss of Cas, while trying to learn what is behind the giant wall. More importantly, she must learn how to get there to keep her promise to the Marked kids. A promise she's so far failed.

But the more she learns, the more she fears.

If Sienna and Theo are going to live for more than a few days, they must do what no Marked kids have ever done. They have to get out of this place.

Help can come from unexpected places. But so can enemies. Traitors lurk where least expected, and Jayla and Sienna must both learn to rely on people they don't trust to stay alive.