It was a former art school used for Himmler's "detention of a special kind". Gestapo headquarters at No 8 Prinz Albrecht Strasse became notorious among Berliners for being on "a particular street you simply didn’t go through.”

He was a close friend of Himmler, who played practical jokes on the Gestapo while spying for the Czechs. The story of Abwehr Captain Paul Thümmel, as featured in my book Operation Second Chance, has to be one of the strangest to emerge from the intelligence annals of the Second World War.

On this day 88 years ago, Hitler took the step which would finally eliminate Germany's army as an institutional obstacle to his plans. The relationship between the 'Bohemian corporal' and the Prussian elite of the senior officer corps had never been easy.

In January 1935, newly-appointed head of German military intelligence, the Abwehr, Admiral Wilhelm Canaris, met Obergruppenführer Reinhard Heydrich, chief of the SS intelligence wing, the SD. The occasion was to sign the 'Ten Commandments' dividing duties between both spy agencies.

The Bendlerblock was not just the headquarters of the Third Reich’s military intelligence. It was the nerve centre of Germany’s internal resistance to Hitler — and the place where the Abwehr quietly undermined the regime from within.