He walked back to St George's-in-the-East, which in his mind he had now reduced to a number of surfaces against which the murderer might have leaned in sorrow, desperation or even, perhaps, joy. For this reason it was worth examining the blackened stones in detail, although he realised that the marks upon them had been deposited by many generations of men and women. It was now a matter of received knowledge in the police force that no human being could rest or move in any area without leaving some trace of his or her identity; but if the walls of the Wapping church were to be analysed by emission spectroscopy, how many partial or residual spectra might be detected? And he had an image of a mob screaming to be set free as he guided his steps towards the tower which rose above the houses cluttered around Red Maiden Lane, Crab Court and Rope Walk.