Nankin, China, 1937.

While all of Europe is in the grip of Hitler's rise to power, at the other end of the world, the Japanese are undertaking to invade China. For thirty years, John Rabe has lived in Nankin, where he manages the Siemens factory that is building a gigantic generator and dam. He is informed that he is being called back to Berlin and that the factory will be handed over to Fliess, a confirmed Nazi for whom Rabe feels nothing but contempt. During the ball to celebrate Rabe's departure, Nankin is bombed by Japanese planes. The inhabitants are terrified and Rabe opens the Siemen factory gates to offer them refuge, hence saving several hundred peoples' lives.

The following day, foreign diplomats discuss the course of action to follow in this critical context and decide to set up a security zone for civilians in Nankin in order to protect the Chinese population. John Rabe is chosen to direct this zone. While the Imperial Japanese Army goes wild and commits brutalities, carries out decapitations, murders, and rapes among the civil population, 250,000 Chinese flock to the security zone. The Japanese plan to find a pretext for attacking it. Thus begins, for Rabe and his comrades, an unceasing struggle.