Commander Stavros Rii of the Kindred is a Sin Eater. Thick, black lines cover his back and neck causing him to feel the pain of others. It is a curse that threatens to shorten his life and makes him unable to bond with a female - not that he's ever found one he wants to bond with. Until he meets Charlie....

Charlie Sayers is an agent with the Earth Protection Bureau (EPB) and anti-Kindred agency dedicated to ridding the world of the big aliens. Charlie joined the EPB out of a sense of patriotism, but she has her own reasons to hate the Kindred.

However, she has bigger problems than the Kindred at the moment. The Enhanced Ones have come to Earth, and they're planning to take over the planet, enslave the inhabitants, and strip them of all emotion. Charlie can't have that, so she agrees to go undercover with Stavros to find the Heart of Love: an artifact which can destroy their mutual enemy forever.

On their dangerous and difficult mission, Charlie learns that going undercover with your worst enemy can rapidly turn him into your best friend...or your lover. Can she hold on to her beliefs and stay true to herself, or will she lose her heart to Stavros? And even if she gives in to desire, will Stav be able to bond her to him? Or are they cursed to be apart forever?