The film is a reflection on the responsibility of man to other people, native nature and the world around us, the problem of preserving Lake Baikal, on the banks of which a large construction project has unfolded. The first half of the 60s of the XX century, the story of the love of young Lena Barmina to an adult respectable person, bearing on his shoulders a heavy burden of responsibility for the activities of a huge enterprise. Construction engineer Chernykh and Lena, the daughter of a scientist, are doing everything to save the lake from harmful and unjustified plums. A difficult relationship develops between them and soon Lena realizes that she is in love. But after learning that Chernykh is married, the girl leaves...

На берегах озера Байкал развернулась большая стройка. Инженер стройки Черных и Лена Бармина, дочь ученого, делают все для того, чтобы сохранить озеро от вредных и неоправданных сливов. Между ними складываются непростые отношения и вскоре Лена понимает, что влюблена. Но узнав, что Черных женат, девушка уезжает...