Alexei Karenin is a solid citizen, a man highly placed in the Russian civil service who leads a regular life of work, dinner parties, and reading. His wife is twenty years younger than he is and beautiful, but it never occurs to him to doubt her fidelity because he has absolutely no inkling of her passionate inner life.
Karenin hears talk around Petersburg that Anna is falling for Count Vronsky and timidly asks her about. She is shocked and horrified. After this discussion, the marriage between the two changes forever: Anna feels injured by Karenin's suspicions, and Karenin can't get over his concern that Anna is sleeping with Vronsky.
Karenin accompanies Anna to a race in which Vronsky is competing. He sees how upset Anna is when Vronsky falls off his horse, and challenges her on the carriage ride home.
Anna confesses that she's having an affair with Vronsky, and Karenin demands that she continue to live in their marriage without drawing attention to her affair. As long as he never has to see Vronsky or hear any gossip about the two of them, he'll be content.
Except – he's actually not content. Knowing that Anna is sleeping with someone else makes Karenin bitter and resentful.
However, when Anna gets sick and asks to see him, Karenin rushes to Anna's side. He has a moment of religious illumination when he decides to forgive both Anna and Vronsky.
Karenin's forgiveness doesn't last that long, though. He becomes increasingly aware that he's the laughing stock of Petersburg society, and he slowly starts to seek refuge in the company of society lady and hypocrite Countess Lydia.
Karenin's career is basically over, though he doesn't know it. His official position is still intact, but everyone knows he won't be getting any more promotions. He thinks he's still doing okay, though, and keeps coming to work telling people how they should be doing things. He continues to work without any inkling of how he's lost the respect of his colleagues with his wishy-washy treatment of Anna and Vronsky.
Countess Lydia convinces Karenin not to let Anna see her son, Seryozha.
Even though he had promised Anna a divorce during her difficult childbirth, when she writes to him to request it now, he refuses, on the advice of Countess Lydia and her psychic.
After Anna's suicide, Karenin adopts her daughter, Annie, to raise with her half-brother, Seryozha.