Plot synopsis: At the end of the war, the old train driver Matys saves his beloved locomotive Líza from depth charges. However, the locomotive is damaged and he is injured. At a critical moment, he stands in for his son-in-law, also a train driver, and thus prevents a train accident. Despite this, he is sent into retirement. To show what the "iron old man" can do, he reconstructs Líza with a group of apprentices...