In the walled-city of Kos, corrupt magi convert a sinner’s wrongs into monstrous beasts. Taj is an Aki, young sin-eater in the magi’s service to dispose of these beasts. However, when an Aki kills a beast, a tattoo appears on their skin and the guilt appears in their minds, which causes Aki to go insane. When Taj is ordered to eat the sin of a royal family member, he is thrust into a conspiracy to destroy Kos. Now Taj must fight to save the princess and his own life.