Simple

"Murder is an abominable act. Therefore, all murderers are an abomination and a blight on the earth. Such disgraces should be removed from society, and will from now on be sent into the Forest and guarded by a Great Wall."
-The New Ordinances

Jake never meant to kill anyone. It was really all in self-defense. But in the New World, murder is murder, even accidents. Five years after being exiled, he still never regretted his decision, though, because it meant his baby sister, now fifteen, is safe. He only wishes he can see her again.
Then, a woman from inside the Wall offers him a job. And if he can complete it, then he can see his sister again and join back into society. It seems too good to be true. He doesn't know what awaits, but he'll do anything for his sister. But when the experiment goes horribly wrong, can he stay alive and keep his partner Tilley alive as well?

Tilley didn't kill anyone. She was shipped off into the unforgiving wilderness after the fatal accident or her twin sister. She wants nothing more than to be back in the safety of the wall, except maybe to have her case review and to finally be proven innocent.
Finally, after ten long years, her case gets reviewed and, if she helps the government, she can reenter society and become an Insider again. She doesn't care what it takes, nothing will be too difficult for her. If only she knew what lied ahead...