Release Me (The New Republic, #2) by Tahereh Mafi

Rosabelle Wolff had a plan. Now she wants revenge. To save her sister she needs to get back home and destroy the system that created her. Rosabelle’s greatest strength is her ability to deaden her mind and body; it’s the only way to survive the surveillance state of Ark Island. But lately her heart has been beating harder; her thoughts are spiraling; her defenses are coming undone.

And there’s only one person to blame.

James Anderson had a plan. Now he has nothing but problems. Rosabelle might be the ally they need in a fight against The Reestablishment, but no one wants to trust an enemy assassin. It doesn’t help that Rosabelle’s not much of a talker, doesn’t work well in groups, and kills people on instinct. Falling for her has cost James nearly everything—but keeping her safe might help save his world.

If only he could convince his older brother.

Aaron Warner Anderson has a headache. Something dark is coming, and Rosabelle’s arrival is just a prelude. In her, he sees shades of himself he can’t trust, and worse: he can no longer get a read on the girl. She’s a dead battery, emanating no emotional feedback. At least not until James walks into a room…

Volcanic romantic tension, breathless reveals, breakneck action—and a dystopian world that never stops raising the stakes: