Whispering Birches is similar in respects to the story of the Vrba-Wetzler report, but ultimately Mihael and Walter are very different characters and intentionally so. In real life, there is no evidence of a link between Franz and Walter although they would undoubtedly have known each other both working around the Materials Section. Rudolf Vrba did testify in Franz Wunsch's trial but mainly on account of the second person on trial Otto Graf. Likewise, there is no evidence of a link between Helena and Walter, although both being Slovakian and working in the same area, they would undoubtedly have known each other. Now the camp is gone and many of its survivors are dead, it will never be possible to validate any such detail. At the end, I felt that making up an escape would have been less respectful to these individuals than to use similar details.
In the story, he is Slovakian, but grows up in Vienna. He went to school with Franz Wolff, but as a Jew was expelled before finishing. After living in the ghetto, his father advises him to escape to his grandfather in Slovakia. He does this in 1938, only to find that the Nazis follow him into Sudetenland (the border country between Austria and Czechoslovakia). He again tries to escape but is caught and eventually ends up in Auschwitz. He joins the Ramp crew, only to find out he is working alongside his old school friend Franz Wolff. He falls in love with Elena who Franz then takes from him.
Mihael is a fiery character full of initiative and sets up the Escape Committee with his Kapo boss Janek. Eventually, he is assigned to the role of Schreiber to Adolf Eichmann's adjutant Lukas Armbrecht and finds out plans of the Hungarian transports. This inspires him to escape with with his friend Alfred Pfizer. On arriving in Slovakia, they then write a report and try to prevent the transports. Betrayed by his people, Mihael sees that there are forces that even he cannot control.