Professor Robert Kuczynski's daughter Ursula, codename Sonya, nicknamed ‘the Mouse’ because of her small, pointed face and ‘feverish inquisitiveness’, was born in Berlin-Schlachtensee on 15 May 1907. At the age of sixteen she joined the Communist Youth League before becoming a fully-fledged member of the KPD in May 1926 and leader of the KPD's Agitation and Propaganda Department (Agitprop) in Berlin's 10th District. Ursula, or Ruth as she preferred to be known, was a ‘Red’ Sally Bowles in a fading Weimar Republic:

Dismissed from her job in 1928 for communist activities, she travelled to New York before returning to Berlin in 1929 to marry her childhood sweetheart, Rudolph (Rolf or Rudi) Hamburger, an architect with communist sympathies. She was twenty-two years of age and Rolf was twenty-six, and they talked constantly ‘about seeing more of the world’:

Shanghai was then virtually a state within a state, divided between the French Concession, the Anglo-American international settlement and the Chinese quarter. Before she left she visited KPD headquarters and informed the comrades of her ‘wish to become active in China’. They greeted her offer with some surprise and incredulity. The city of Shanghai was in the grip of a ‘White Terror’ and China itself close to civil war. Three years earlier a strike of Shanghai workers had been brutally suppressed by a Chinese warlord backed by French and British troops. Two hundred Chinese had been decapitated in the streets, their heads stuck on bamboo poles or displayed on kitchen platters; the Chinese Communist Party had been outlawed. Was she fully aware of the dangers involved? Looking back she could understand their incredulity.