Dorril, Stephen. MI6: inside the covert world of Her Majesty’s secret intelligence service. Free Press, New York - 2000
Accounts on Walter Schellenberg p.101 (Karl Marcus sent in France as peace feeler to Lord Vansittart), p.106 (opinion of British intelligence officer Stuart Hampshire over Schellenberg following his interrogation), p.168 (MI6 claims that Van Heulen met with Dulles and WS and Dulles would have spoken to Prinz Max Hohenlohe, his 20 yars friend, for a ‘Greater Germany’ including Austria and a section of Czechoslovakia as part of a ‘cordon sanitaire against Bolshevism’), p.208 (The Wannsee Institute wherefrom the sinister conference took its name, was considered by Schellenberg as one his most successful achievements), p.411 (account of Anthony Blunt and cleaning of Max Klatt by WS from being a soviet agent), p.418 (Karl Marcus background along Schellenberg, + Rote Kapelle details).
A book with a lot of details on many things but never acknowledging enemy successes even when, like the Venlo incident, it had repercussions on its chief Menzies career and on its approach to the war is a good documentary source but it is, unfortunately, not the work of an enlightening historian on the subject. The book illustrates the lost opportunity to give us a synthetic view of the war under the MI6 angle.