In The Heart to Kill, Cassie and Evan wake up together. He goes hunting for a bit, scaring her when he returns and leading her to confront him with a gun before realizing who he is. Cassie realizes she has feelings for him. Evan talks about his girlfriend Lauren who hung herself and says he thinks Sammy is alive, since Cassie would feel it otherwise. They kiss and snuggle until they fall asleep.
Cassie begins to feel suspicious of Evan, realizing that he never comes back with the things he has hunted and that he has very smooth hands for a farmer's boy. Cassie looks through his house for proof and finds family albums confirming his story, but she also finds her M16 which she lost when running from the Silencer.
As she turns to run, she runs into Evan. She confronts him and Evan says he found it by the highway. Cassie is reluctant to trust him but does and Evan reveals that he doesn't have something to live for, but he does have something to die for.
In The Spirit of Vengeance, Squad 53 goes on their first mission in the field. They fly in on a Black Hawk helicopter and take down three infesteds. Oopma is hit by a sniper and dies from his injuries even after Dumbo tries to save him. The squad is angry at Ben for Oompa's death, but they band together to get away from the sniper.
Ringer and Ben talk. Ben removes Ringer's implant at her request and sees her head light up green through the special goggles they were given. They realize that people who glow green aren't Others, but humans. The equipment reacts when there is no chip implanted in someone's head. They are horrified by the news and quickly remove Ben's chip as well.
Ringer and Ben leaves their implants and go after the sniper. They are curious to find out who it is and are shocked to discover Reznick. Ringer kills him. They find a computer next to Reznick showing the location of their implants and those of each of the other squad members.
They tell the rest of the squad their findings. They are initially reluctant to believe what they are told, but then they cut their own implants out. The squad agrees to all go rogue together, but Ben has to go back for Sammy. Ringer shoots Ben to make it believable that he was left behind. Ben is interviewed by Vosch, who has huge suspicions about Ben. Unconvinced by Ben's story that everyone went Dorothy, or crazy, but Ben, Vosch plugs Ben into Wonderland again to learn the real truth.
Cassie is falling for Evan very quickly. She is uncertain if she can trust him, but finds herself very confused. Evan shows his skill at manipulating Cassie. Regardless of whether he is telling the truth about dying for her, he is able to convince Cassie that she should lower her weapon.
This would have been unthinkable in the first chapter of the book when we first met Cassie. There, she was inseparable from her gun. Cassie shot the Crucifix soldier simply on the suspicion that he had a gun and might betray her.
Evan has already shown himself as duplicitous and sneaky, yet Cassie still does not shoot him. She has changed a great deal since she met Evan. Evan also seems to imply that Cassie has changed him a great deal. He now has something to die for, which gives him a purpose in life. The only unclear issue is whether or not Evan is telling the truth, or simply lying to save himself.
In The Spirit of Vengeance, the point of view shifts back from Cassie to Ben. Ben and Ringer manage to overcome the indoctrination they experienced at Camp Haven/Wright-Patterson and they realize the truth. This moment marks that both have come full circle - from being naive, trusting children, to wide-eyed adults.
Both Ringer and Ben take on the mantle of leaders, trying to get both their squad and Sammy to safety. This chapter shows how close they have grown, as well as exposes the true nature and goal of the Others: to use the children as the fifth wave.