Velká přehrada.

Young engineer Petr Pavelec works on a dam plan on the Loučnica River. He meets Irena, the daughter of an unscrupulous construction entrepreneur Berka, and falls in love with her. When Petr's project wins the tender, Berka and Irena take him on as a partner, and the company is awarded the contract to build the dam. Petr, in love, does not see how sloppy the construction is being carried out. He only sees it when a worker is killed on the construction site...