Forty years ago the Spirit of Vengeance—a Purpose—took William Morgan as its host, demanding he avenge the innocent by killing the guilty. Since then, Will has retreated behind Gar, a façade he uses to avoid dealing with what he's become. Cold, impassive, and devoid of emotion, Gar goes about his life alone—until his tidy, orderly world is upended when he meets Ryan, a broken young man cast out by his family. Spurred to action for reasons he can't understand, Gar saves Ryan from death and finds himself confronted by his humanity.

Spending time with Ryan helps Will claw out from under Gar's shadow. He recognizes Ryan is the key to his reclaiming his humanity and facing his past. As Will struggles to control the Purpose, Ryan challenges him to rethink everything he knew about himself and the spirit that possesses him. In the process, he pushes Will to do something he hasn't done in decades: care.