Your Knife, My Heart by K.M. Moronova

Here is a summary with spoilers for Your Knife, My Heart by K.M. Moronova

Emery Maves finds herself in an impossible scenario. She has been in prison for years, though she has escaped a death sentence. She now finds herself on a train, still a prisoner, but this time with an opportunity to get out and have her freedom back, and her life wiped clean. The commander who picks her up mentions that there is an elite team, and she is going to compete in something called the Under Trials. If she wins and continues to serve, then she can have her freedom. Though the commander does not have much faith in her to begin with, he will if she can last her first night.

On arrival, Emery meets her new partner, Cameron Morten. He has a reputation for killing all of his partners, and now no one wants to be with him. As the two are left in a room together, Cameron is drawn to her for some reason, but that does not stop him from trying to kill her. They have a fight, where Emery holds her own, but she later finds out she will lose because Cameron cannot feel pain. The two put on a temporary truce for the night. Cameron tells her that the military has been experimenting on him with a pill that makes him unable to feel pain. He has survived years on the pill, and no other soldier has been able to do that. They keep him around so they can keep studying him.

Emery manages to survive the night, and she and Cameron are officially brought into the Under Trials, which are designed to break them. The two keep their truce up, though Emery is worried that if Cameron sees a chance, he will kill her. They make some enemies on their first day, but they both manage to establish some dominance. What does not help either of them is that they are forced to share a bed as partners, and it often leads to Emery waking up in Cameron’s arms. Soon, she finds that Cameron wakes up early each day, and now she wants to know why. She finds him one morning and realizes that he is still taking the pill. He is addicted at this point. The pills are affecting him, including making his blood turn black. Emery continues to watch him until he faints, and she runs to help him. He tells her that he is fine, but then admits he has some feelings for her. In that moment, she realizes she also has some feelings for him. This leads to the two of them sleeping together for the first time, just moments before the Under Trials officially begin.

Everyone is taken to the Alaskan wilderness, where the first trial starts. There are no rules, and everyone can hunt other people. After some time apart, Cameron and Emery finally find each other and are able to make it through the first trial. The second trial allows them to start together and work together, though they have some issues when the pills become a problem for Cameron. In the final trial, they are a group of five, and in order to win, they all must make it to the end, dead or alive. During that time, Emery gets injured, and Cameron takes the moment to give her a pill; she can no longer feel any pain. Emery is upset by this but also intrigued. She wishes that the pain pill worked for mental pain, because she watches one of her friends, Bree, die. She goes to kill the man who did it, Bryce. She finds out that Bryce works for her very influential father. Bryce was sent by her father to protect her, and he plans to tell her more, but then an explosion hits and knocks Emery out.

When she wakes, she sees a handsome man next to her in her hospital bed, and she has no recollection of who he is.