Rathenau had been a close personal friend of his father's: the shocking event and the rising tide of right-wing extremism, which was particularly hard to miss in Munich, demonstrated the fragility of the new liberal-democratic political order.
Shortly before they left Berlin Ursula's parents organised a dinner party to which they invited Hellmut Wilhelm, the son of a celebrated (but recently deceased) "China expert".
It is nevertheless more than possible that the contemporary social and political realities of the situation in Shanghai, the extent to which the city had become a cultural melting pot, and indeed the way in which it had become a magnet for international espionage, only became apparent to the couple once they arrived in their new home-city.
In the early part of 1932, the worsening political climate in Germany and complaints lodged with the German consul in Shanghai by Chinese nationalists led the Frankfurter Allgemeine to dispense with her services.
Till now the Hamburgers had been living in rented accommodation, but they now acquired a house of their own, moving into a large terraced property at Avenue Joffre 1676, in a notably verdant part of the French Concession in April 1931.
Rudolf (according to his wife's subsequently published autobiography) had by now become a convinced communist and was keen not to remain "politically inactive" for any longer: Ursula informed her Moscow handlers of this development.
For the GRU handlers, organising the documents necessary for a young middle-class architect and his family to move to Poland, and integrating them appropriately in Warsaw, would be far less of a challenge than arranging for the settlement of a single mother with two small children.
[3] The return to Europe at the end of 1935 gave Rudolf Hamburger his first opportunity to stop off in Moscow and meet the leaders of the GRU, for which he had already worked in a succession of difficult situations, without having had direct contact with an intelligence handler.
His status as a foreign correspondent may have reduced the obstructiveness the couple encountered among officialdom when applying to extend their residence permits, and enabled them to lead a relatively conventional middle-class existence.
However, the Chinese communists had left Shanghai in 1937 when, following months of bitter fighting, the city (apart from the International Settlement and the French Concession) had been placed under Japanese military occupation.
The alternative route, approximately three times as long, involved travelling by ship to Hong Kong, from where it would be possible to take a flight to Chongqing, Chiang Kai-shek's wartime capital between 1937 and 1946.
Here he had problems with the English border officials because he was travelling on a Honduras passport., but after an involuntary stay of several hours he was able to catch a flight for Chongqing where the Chinese authorities found and confiscated his radio for inspection.
[2] Meanwhile, Otto also used his own contacts to try and secure Rudolf's release, invoking the help of a senior nationalist Chinese government official who was in Shanghai at the time whom the Hamburger brothers both knew well.
Wong Pin Fong communicated his own unremarkable conclusions: "Foreigner ... in reality you can really only be a member of the American or Soviet secret service" ("... eigentlich kannst du nur zum amerikanischen oder sowjetischen Geheimdienst gehören").
[1] Hamburger was keen to continue to Turkey as instructed, but with international tensions rising in the area the Turkish authorities reacted negatively to his Honduras passport, and he encountered difficulty obtaining a visa.
Another European was hired to supervise the project, though Hamburger himself was also closely involved in co-ordination with the various parts of the ministry, His boss was a doctor-engineer who had trained in Germany who "came from one of the leading families in the land".
They did not find the heavy radio receiver-transmitter he had been given by his Soviet handlers, which was kept in an aluminium container the size of a small suitcase, and which was hung casually with a lot of knitting up a disused chimney.
The authorities established that stamps placed in it by passport officers in three British colonial - Bombay, Singapore and Suez - could not be matched to any corresponding records in the files of the checkpoints involved.
Although it might be thought that his contribution to Soviet intelligence had been less than stellar since 1930, and the GRU had given little reason to believe that they valued his services very highly, Rudolf Hamburger had demonstrated a remarkable degree of persistence, commitment and loyalty over the years.
Many years later the East German homeland security service (MfS) came to hold an information report from the Soviets which included the conclusion "The circumstances of Hamburger's release from detention in Iran gave rise to the suspicion that he had been recruited by a foreign intelligence service" ("Die Umstände der Entlassung Hamburgers aus der Haft in Iran erwecken Verdacht seiner Anwerbung durch einen ausländischen Geheimdienst").
Seit den dreissiger Jahren hat das damalige Volkskommissariat für Innere Angelegenheiten Drei-Mann-Ausschüsse, sogenannte OSO, mit Sondervollmachten eingesetzt.
At right angles to the long side walls, in pairs, sets of double-deck bunk beds ... arranged in a way that takes no account of the positions of the windows, due to the shortage of space, and therefore these are partially obstructed and only let in half of the light.
In Rudolf Hamburger's case, that meant that his remaining three-year sentence would apparently be reduced to one and a half years when he arrived at Kuybyshev (since 1991 again identified officially by its pre-1935 name as Samara).
[2] Stoll had been sentenced (without trial) to a ten year term in Siberia in 1950 following a complicated series of events involving espionage allegations and political activism in the Soviet sponsored German Democratic Republic.
There was, naturally, no mention of labour camps in his contribution, which concluded on a resolutely positive note: On his release Hamburger moved to a small Ukrainian city where he lodged with a farmer's wife identified as "Galja".
Eighteen months earlier, in August/September 1952, the two former Poelzig student Richard Paulick and Kurt Liebknecht had travelled as part of a delegation of East German architects undertaking a round trip of the Soviet Union.
However, he had lived outside Germany since 1930, and much of his more exotic international travel had been undertaken on behalf of Soviet intelligence: most of the "usual sources" on political involvement between 1930 and 1955 were not applicable or not accessible, even to East German state agencies.
[17] Ursula Kuczynski (Ruth Werner) had also performed her espionage activities under conditions of great secrecy till 1950, but after the trial of Klaus Fuchs it became impossible to pretend that she had not been a spy.
But Hamburger's objective, to draw the reader closer to the truth about his experiences in the labour camps, is impressively achieved ... As a historical testimony the book is depressing, but it is also uplifting in its irrepressible hope for humanity.
[2] Till now there had been powerful institutional barriers preventing Rudolf Hamburger's footprint from appearing in the historical record except as a footnote in his wife's remarkable story.