Told in stark, unsparing detail, Haffner's story delves into the illicit underworld of Berlin on the eve of Hitler's rise to power, describing how these blood brothers move from one petty crime to the next, spending their nights in underground bars and makeshift hostels, struggling together to survive the harsh realities of gang life and finding in one another the legitimacy denied them by society.

Blood Brothers is the only known novel by German social worker and journalist Ernst Haffner, of whom nearly all traces were lost during the course of World War II.