As the Second World War progressed and defeat for Hitler’s Third Reich in all theatres became ever more certain, the tight Abwehr network, built so effectively by its head, Admiral Canaris, began to unravel. High-level defections to the Allies and bitter disputes with the Sicherheitsdienst (SD) added to a collapse in morale. Most notably was the increasing opposition within the officer ranks of the Army to Hitler fermented by Canaris and his deputy Generalmajor Hans Oster.

The final years of the Abwehr were marked by the Abwehr’s efforts to undermine the regime, which came to a bloody conclusion following the Valkyrie assassination attempt of 20 July 1944. This saw the arrest of many Abwehr officials and the execution of Canaris and Oster.

In this penetrating study of the final years of the Abwehr, Nigel West, a world-renowned specialist in the field, pieces together the gradual decline in the organization’s role and importance with Hitler and his acolytes paying little heed to reports that were increasingly cautionary.

Among the many previously undisclosed stories are details gleaned from recently opened files which tell of a hitherto unknown spy-swap. This was the exchange of Berthold Shulze-Holthus, a German spy detained in Iran, for Ferdinand Rodriguez, a British radio operator captured in France. This was the only such exchange that took place during the whole of the Second World War – though the fact that the swap took place at all suggests that a previously unsuspected degree of communication existed between the Allies and Nazi Germany.

Perhaps most tantalizingly of all, is the new night light thrown upon the role the British Secret Intelligence Service, MI6, had, in league with the Abwehr, in the Valkyrie bombing which almost killed Hitler.