Book
Blood Enemy
Book 4 in the The Warsaw Quartet series.
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In June 1944, a Wehrmacht war-crimes investigator and his escort are killed in an ambush attributed to the Polish resistance. Jan Kalisz doubts the obvious explanation and receives reluctant permission to investigate as German confidence weakens before the approaching Red Army.
The search takes him through bomb-damaged Berlin and to Auschwitz-Birkenau, where a witness is held and Josef Mengele represents a danger beyond the original case. Kalisz returns to a Warsaw preparing for uprising after five years of feigned collaboration. To expose the killers and protect his family, he must decide whether the moment has come to reveal his allegiance and accept the consequences of open resistance.