The film tells how in the iron blockade of the blockade worked "the blood factory", the Institute of blood transfusion that provided the Leningrad front and the city in this strategic resource: blood donation. The blood bond between the city and its defenders was a very important factor in breaking the blockade and finally crushing the enemy. Due to a prolonged lack of food and a very great psychic stress the blood of the inhabitants of Leningrad has undergone phenomenal biochemical transformations which have had consequences for the following generations. The hypothesis confirmed by the latest research by geneticists and biologists is that this 900-day "forced fast" suffered by people during the blockade gave a post-war generation with a specific mentality and a spirit of sacrifice of the inhabitants. from Saint Petersburg.