[2] He later served attempting to counter the American advance into Germany, hiding in barns or ruined houses when necessary, and once carrying a machine gun on his back for three days to Bitterfeld before eventually being captured and becoming a prisoner of war.

[1] Injured, he spent several weeks in a prisoner of war camp before being sent as a civilian worker to a farm at the Abbey of Fontenay in France for three years.

He found the book to be full of errors and resolved to write a more accurate account[1] despite most of the official records of the period being closed,[3] meaning that he relied heavily on personal interviews with witnesses.

[4] The resulting book, Geheimauftrag Irland: Deutsche Agenten im Irischen Untergrundkampf 1939-1945, was published in 1961 and was the first survey of the activity of Nazi spies in the Republic of Ireland before and during the Second World War.

[6] It received wide publicity as journalists translated sections into English and Stephan wrote supporting articles in Irish newspapers.

An English language translation was published as Spies in Ireland in 1963[5] and serialised in the Irish Sunday Independent newspaper the same year.

[3] The detailed information about individuals caused embarrassment to the German embassy in Ireland, some of whose staff were in post during the war and suspected of spying, while Helmut Clissman, one of the sources for the book and by the 1960s an Irish citizen and established businessman in the country, was revealed to have been an Abwehr officer during the war[3] whom the Nazis twice tried to smuggle into Ireland to work with the Irish Republican Army against the British.