Rikar: The Sanctuary Series, Book 2 (Unabridged‪)‬

After Rikar's abduction, he finds himself once again fighting for his life in the gladiator arena called the Kingdom. Some of his genetically mutated foes are so far gone they can only be described as monsters. Rikar is forced to undergo the life-altering Nano treatments, and he fears he will become just like those he fights. As his sanity slowly dissolves, the only peace he finds is with beautiful fellow prisoner Lindsay.

Lindsay was sold by her family to Vulnitro years ago, and has been imprisoned in the Kingdom ever since. She and her friends live on Victors' Row, and their sole purpose is to reward the winners of the arena. Lindsay is tired of seeing Nano experiments turn good men into monsters. Every day is a fight for dignity and survival from these brutes. She's given up hope of a normal relationship, until she meets Rikar, and decides to help one man fight his Nano curse.

Does Lindsay dare to fall in love in a place like the Kingdom? Even if they could escape, where would they go? Is any place safe for people like them? 

This is the second book in the Sanctuary series. While each can be listened to solo, I recommend listening to the first one to understand the full storyline.