In Sin Sick, Joshua Pederson draws on the latest research about identifying and treating the pain of perpetration to advance and deploy a literary theory of moral injury that addresses fictional representations of the mental anguish of those who have injured or killed others. Pederson's work foregrounds moral injury, a recent psychological concept distinct from trauma that is used to describe the psychic wounds suffered by those who breach their own deeply held ethical principles.

Complementing writings on trauma theory that posit the textual manifestation of trauma as absence, Sin Sick argues that moral injury appears in literature in a variety of forms of excess. Pederson closely reads works by Dostoevsky (Crime and Punishment), Camus (The Fall), and veterans of the wars in Iraq and Afghanistan (Brian Turner's Here, Bullet; Kevin Powers' The Yellow Birds; Phil Klay's Redeployment; and Roy Scranton's War Porn), contending that recognizing and understanding the suffering of perpetrators, without condoning their crimes, enriches the experience of reading—and of being human.