Bengt von zur Mühlen, the founder of Chronos-Film, has been particularly generous with archival footage and taped interviews of participants. I am also greatly obliged to Gerald Ramm and to Dietmar Arnold of Berliner Unterwelten for their help.

I am truly grateful to all those who aided me so much during my travels with advice, introductions and hospitality: in Russia, Dr Galya and Dr Luba Vinogradova, Professor Anatoly Aleksandrovich Chernobayev, and Simon Smith and Sian Stickings; in Germany, William Durie, Staatssekretar a.D. Karl-Günther and Frau von Hase, and Andrew and Sally Gimson; in the United States, Susan Mary Alsop, Major General and Mrs Charles Vyvyan, Bruce Lee, Mr and Mrs Charles von Luttichau and Martin Blumenson.

It has been a great pleasure for me, as well as extremely useful for the book, to work in partnership with BBC Timewatch. I am deeply grateful to Laurence Rees, whose idea it was, to Dr Tilman Remme, in whose company I have most enjoyably learned a great deal, and to Detlef Siebert, who generously helped so much at an early stage with advice and interviewees. Others who have also provided introductions, information, help and advice include Anne Applebaum, Christopher Arkell, Claudia Bismarck, Leopold Graf von Bismarck, Sir Rodric Braithwaite, Professor Christopher Dandeker, Dr Engel of the Archiv der Freien Universitat, Professor John Erickson, Wolf Gebhardt, Jon Halliday, Nina Lobanov-Rostovsky, Dr Catherine Merridale, Professor Oleg Aleksandrovich Rzheshevsky, Professor Moshe Schein of the New York Methodist Hospital, Karl Schwarz, Simon Sebag-Montefiore, Gia Sulkhanishvili, Dr Galya Vinogradova and Ian Weston-Smith.

This book, quite literally, would never have been possible in the form it takes without the wonderful help I have had from Dr Luba Vinogradova in Russia and Angelica von Hase in Germany. It has been a privilege and a pleasure to work with them. I am also extremely grateful to Sarah Jackson for all her work on photographic research, to Bettina von Hase for supplementary archival research in Germany and to David List in England. Charlotte Salford very kindly translated the documents from the Krigsarkivet in Stockholm for me.