Chill factor.

Hennessey and Yellich are looking for a Mr. Big. A corpse is discovered in the middle of the city of York. Male; no identification. Shot. And tortured before his murder. A professional hit, by the look of it. Gradually people talk; hints are dropped and trails appear - all leading to a man with no record and who has never been inside a police station. But the police know him - he's connected to another unexplained death. And another. And a few more.