Batalov is a Soviet nuclear physicist working in Siberia with his professor, Plotnikov. In an accident both men are exposed to dangerously high amounts of radiation, causing Plotnikov's death. Batalov is warned that further radiation will kill him as well, but his work is far too important
to him to give it up for a safer job. His devotion to his work affects his relationship with Lavrova, who nearly leaves him for a mutual friend (Smoktunovsky), but he rallies and finally marries Batalov. Smoktunovsky, in the meantime, comes to work with his friend. When Batalov makes another
important breakthrough and is once more exposed to radiation, he swears Smoktunovsky to s...