Rafe Spall
I've noticed Rafe Spall in a bunch of things over the years - Shaun of the Dead, Green Street, Hot Fuzz etc but this has to be his best role to date.
His character, Jay, is a truly memorable pyscho. He is somehow likeable in a boyish way but terrifying underneath. The two scenes in episode 2 with the garage owner and then Andy's pregnant girlfriend were genuinely unsettling.
Someone else mentioned The Killing and Spiral and I think Shadow Line is proving we that UK TV can produce that sort of quality crime drama with a strong cast delivering great performances.
I am a big fan of Chiwetel Ejiofor and Christopher Ecclestone but I think it is going to be Rafe Spall that gets noticed here.