It is late April 1986. Maryana, a doctor, decides to pay a weekend visit to her relatives in Pripyat. She takes her younger sister, high school student Alya, with her. On the way there the girls see a terrible explosion at the Chernobyl nuclear power station.

Evacuation is announced in Pripyat, but Alya stays in the city because she wants to find out all about her father. Unfortunately, during the flight to the burning reactor his helicopter crashes and Nikolay dies. The girl finds out about his death from Pasha. She is in despair and begs him to stay and not leave her all alone.

By a miraculous combination of events Pasha is transported to a hospital in Moscow where he receives treatment. Alya follows him and begs the doctors to let her see him. She still believes that her profound love will save his life. Unfortunately, Pasha cannot be saved. In the same hospital Maryana, Alya's sister, also dies. In Kyiv, Alya's grandfather passes away after a heart attack.

Pasha feels better and runs away from the hospital to fulfill a promise given to Alya and see her again. The lovers spend a whole day in a totally empty city. Despite chaos and death reigning around they are happy. But in the morning Pasha feels unwell. They decide to leave the city on foot to find help...