Very early on a July morning in 1919 Constable Brown was on his beat in Kensington, in the immediate neighbourhood of Cathcart Square. Cathcart Square was an old-fashioned backwater of this highly respectable suburb. It had not been built on any regular lines. Small, narrow houses nestled comfortably by the side of what might be called mansions. At the entrance to the Square itself, a narrow-fronted milk-shop stood next door to a palatial residence. The dairy was very old, and the Square, with its strange agglomeration of houses, had been built round it.