[1][2][3] The film tells about the twin brothers, one of whom enjoys comfortable life in Moscow, being a banya employee who has "influential" clients, and the other works as a fishing inspector in his native village.
[4] Ivan Sergeyevich Kashkin (played by Leonid Kuravlyov) is a Moscow-based bathhouse attendant with an impressive list of influential clients who can provide access to scarce goods.
His twin brother, Sergey Kashkin (also played by Leonid Kuravlyov), is an honest provincial inspector for the Fish Protection Agency, known for his strictness with poachers.
When Sergey ends up in the hospital, he asks Ivan to fill in for him temporarily so that poachers won't take advantage of his absence.
The local factory continues dumping industrial waste into the river, and combined with the activities of poachers, this causes a massive die-off of sturgeon.