Katerina is lonely. She is married to a merchant, Zinovy, but they have no children. Her father-in-law Boris is horrible to her and blames her for not having any children. When Zinovy goes away on business Boris forces her to swear to be faithful (not to make love to any other man while her husband is away). However, one of the servants, Sergei, becomes her lover. When Boris finds out he is furious and whips Sergei and locks him up. Katerina poisons Boris with mushrooms. When he dies she gets the key from his pocket and frees Sergei.