A murdered priest. Five suspects - all nuns. It's a cold foggy night, deep in the Yorkshire moors. In a small convent, a priest is discovered dead - blood staining his collar and covering his face. Father Morgan was stabbed viciously to death by someone within these very walls. With just five nuns living in the convent and no sign of a break-in, Detective Inspector Angel assumes this will be a straightforward case. But Angel hasn't counted on the bloodlust of this ruthless murderer. Two of the nuns are killed just days later - stabbed in their beds as they sleep. And then there are just three nuns - all seemingly innocent . . . Angel must act fast to solve this baffling case. The clock is ticking. Can Angel catch the killer nun before any more innocent lives are lost? Or has he finally met his match?