Lawn Road Flats, also known as the Isokon building, comprises 32 units of equal size in Lawn Road, Belsize Park, North London. It was, and remains, a remarkable building with an equally remarkable history.

The name, Isokon arose from the architect Wells Coates' use of isometric perspective in his drawings and, as the Lawn Road Flats were to be in ‘a form of modular units, “Isometric Unit Construction” soon became Isokon’. While this was not the first modernist building in Britain – that accolade should go to ‘New Ways’ in Northampton, a whitewashed, cement-rendered, two storey structure with a crested parapet, designed by the German architect, Peter Behrens in 1925 – the construction of the Isokon building was the first time reinforced concrete was used in British domestic architecture.

On the face of it, the Isokon building is a curious subject for an intelligence historian but the idea for this book was sparked by a paragraph in The Mitrokhin Archive, an account of the KGB, written by Christopher Andrew and Vasili Mitrokhin. There, the Austrian communist spy Arnold Deutsch, controller of ‘The Magnificent Five,’ the five Cambridge graduates who spied for the Soviet Union between 1934 and 1963, is found living in Lawn Road Flats, next door to the crime novelist Agatha Christie: