Your face is a blur to him. But your body still bleeds.

The Farren family has been a plague upon Philadelphia's most dangerous neighbourhood, the Devil's Pocket, for generations. There, row after row of tumbledown houses hide dark secrets - none darker than Billy, the youngest Farren.

Afflicted by a syndrome that means he can't recognise faces, Billy must use photographs to identify his family - and his victims. And when your life has bled away, he takes a final, gruesome picture for his wall.

But what is the meaning of the horrific ritual Billy enacts with every murder? And is there any connection to a childhood event Detective Kevin Byrne has buried so well it's hidden even from his former partner Jessica Balzano?