Based upon a true story, the movie centers on the German communist Robert, a "Kapo" in a concentration camp. When some Polish children are brought to the camp, Robert tries to save them from certain death. Due to his efforts they are being trained as masons and become part of his construction gang. Nevertheless, the boys, and mainly the clever Janusz, are very suspicious of Robert. They have already experienced too much evil and do not want to trust anybody – least of all a German.