Anna Karenina's such a masterful novel that it's got two complete main plots for the price of one. We're going to outline them both here. We can't help but notice that the plots are in a lot of ways mirror reflections of one another. As Anna's life goes downhill, Levin's goes up, and what makes Levin happy (i.e., his family) is exactly what makes Anna miserable.
Anna's so into family that she intervenes in someone else's marriage. Levin, meanwhile, wants a family and is frustrated that he doesn't have one yet.
Anna: The initial stage of the novel is the status quo at the beginning of the book, before the events of the plot start taking place. At the outset of Part 1, Anna Karenina is so big on family life that she gets called in to bring her brother and his wife back together. This is also the first time she's ever been away from her son since his birth, and she misses him desperately—another sign of Anna's commitment to the family as an institution.
Levin: At the beginning of the novel, Constantine Levin is frustrated and confused. He has two great goals: to reform Russia's agricultural system and to marry Kitty Shcherbatsky. But he hasn't made significant progress on either front.
Anna meets Vronsky and starts feeling unsatisfied with her family life. Levin attempts both farming and marriage proposing, and fails at both.
Anna: The conflict of the novel is where something happens to shake the major characters out of their status quo. In Anna's case, she meets a certain Count Vronsky while traveling from Petersburg to Moscow, and then again from Moscow to Petersburg in the later chapters of Part 1. Although Anna hasn't done anything with him yet, it's clear that this is the beginning of the end for her. She becomes frustrated with her family life, noting with disappointment that even her beloved son seems disappointing when she gets home (in Chapter 32).
Levin: Levin encounters lots of conflicts through the middle and ending chapters of Part 1. His quest for a wife is frustrated when Kitty turns him down in favor of Vronsky. What's more, he can't seem to clarify his views on agriculture for any of his sophisticated friends and relatives. Levin's conflict is the reverse of Anna's. Where Anna has a family that she's about to give up, Levin wants a family (and an intellectual life) that he's being denied.
As Anna's dissatisfaction with her own marriage mounts, she turns more and more to Vronsky. Levin continues on his quest to resolve his existential angst through marriage and farming.
Anna: The complication of the plot usually means the intensification of what's already there. So, Anna's already started to turn away from Karenin in her heart, and her disappointment when she gets back to their house in Petersburg signals this increasing distance. What makes their separation inevitable, though, happens in Part 2, Chapter 9, when Karenin confronts Anna with his suspicions about her feeling for Vronsky.
Anna had been feeling guilty about her conduct with Vronsky, but once Karenin accuses her, she feels like she's got the moral high ground. Karenin has proven (in Anna's mind) that he doesn't sympathize with her struggles. It's almost like she's saying, "If you think so badly of me, I'm just going to go for it!"
Levin: If Anna's plot deals with the loss of family, Levin's on a track to getting one—but he has to suffer a bit first. So he's proposed to Kitty and been turned down. He's also asked his peasants to help him reform but, again, been refused. During the beginning of Part 3, we see the intensification of his desire for both marriage and the agricultural life he thinks will support his perfect family.
Levin meets up with Dolly, Kitty's sister, who convinces him (almost against his will) that he'd have a better shot with Kitty this time around. And he encounters a peasant, Ivan Parmenov, and his family in Chapter 11. Levin realizes that, even though he can't have a peasant's life, the open, easy affection of the Parmenov family is still his ideal.
Again, Levin's view that family and economy should support one another gets reaffirmed in this section. And the fact that he has neither family nor a functioning estate leaves him extremely unsatisfied by the end of Part 3.
Anna suffers an irreparable break with Karenin and ties her fate forever to Vronsky. Levin finally gets the girl.
Anna: We've reached the climactic sections of the plot, when each of our two protagonists reach a conclusion about their respective issues. Anna's on track to destroy her family, so the climax is the moment of no return, when everything falls apart. This part of Anna's plot comes much earlier in the novel than Levin's corresponding climax. In the latter half of Part 2, Anna attends a horse race with Karenin in which Vronsky is participating. (She's also discovered that she's pregnant with Vronsky's child, but that's not what compels her to confess all to Karenin.)
When Vronsky is thrown from his horse, Anna's visible distress tips off Karenin that all is not well with Anna. On the carriage ride home, Anna's so filled with disgust for her boring, distant husband that she tells him exactly what she's been getting up to with Vronsky while Karenin's off being busy and important. Once everything is exposed to Karenin, all that's left to figure out is what he's going to do next.
Levin: We get a much longer development for Levin's climax because so much of his plot is occupied with philosophical and political arguments about the Russian peasants and the nobility. Those arguments are important because they give substance to Levin's existential angst and because they explain why marriage and the agricultural life are so important to him—but they don't get us to his climax any quicker.
This is why his engagement to Kitty doesn't come until Part 4, Chapter 13. The book is setting out a host of problems for Levin including the zemstvos, And the relation of religion to private faith. Levin's attitude towards these issues turns on whether or not he has Kitty. The narrative spends a lot of time showing how much complicated stuff is inside Levin so that we see exactly what's riding on this marriage.
What is Karenin going to do about his wayward wife? And now that Levin is married, is he finally satisfied?
Anna: So, Anna's thrown in her lot with Vronsky. Now what? We're on the edges of our seats wondering what Karenin's going to do about all of this. And Karenin keeps us in suspense, because his decision is to do nothing. He decides not to divorce Anna. And when Karenin forgives Anna (when he thinks she's going to die), Anna won't ask for a divorce. And when she does ask for a divorce, Countess Lydia has already convinced Karenin to go back on his word.
Over the course of the next four parts of the novel, Anna's kept perpetually in limbo, unable to change her situation with either Karenin or Vronsky. At this point in the story, we have no idea what it will take to make a real change in her life now that she's severed her relationship with her original family.
Levin: Meanwhile, Levin, also spends the next four parts of the novel (after Part 4) in suspense. He's married now, so, are his existential doubts gone? Not at all. He's discovered that, even though he loves his wife, they fight all the time. His brother Nicholas dies, and he learns nothing grand about the meaning of life. He starts gambling, spending money, and falling for Anna.
Thankfully this behavior doesn't last. Levin's son Dmitri is born, and Levin is a bit disappointed. He thinks the kid looks kind of pathetic—nothing to answer all of his big questions. As with Anna's section, it's almost as though Levin himself is waiting for something to step in and change his life for him. He thought it would be marriage, and while that has made him a better man, he's still searching. But for what?
Anna commits suicide; Levin has an epiphany.
The denouement is the plot stage when everything comes out in the open and all is revealed to the reader. Despite the fact that both Anna and Levin appear to have gotten what they wanted—Vronsky and Kitty, respectively—we are still in suspense about what long-term effects these life changes are going to have.
Anna: In Anna's case, the effects are all bad. Having gotten Vronsky, she's had to give up everything that made her life meaningful: the respect of society, the love of her son, the association of other good women. At this point, Anna has an epiphany that she needs to ask for God's forgiveness, and then she kills herself. At that key moment on the train station at the end of Part 7, she sees an opportunity to take control of the life that has become so dependent on Vronsky. And her final exertion of self-control leads to her death.
Levin: The answer to all of Levin's questions comes at the end of Part 8, when he encounters an old peasant who distinguishes between living for one's survival (which is natural), and living for good. This addresses Levin's existential angst throughout much of the book: he's had lots of ideas about how family is key to making individuals good, but he'd never been able to make that match up with his less personal concepts of agricultural reform.
Now he realizes that giant theories about The Russian Peasant are less important than behaving instinctively according to the good in his own nature. He's seen Kitty do this loads of times, and now he wants to do the same: he wants to put good into his own life, as a family man and a landlord on his own estate.
Anna is dead. Levin embraces his love for the family he's been looking for throughout the novel.
Anna: So it's all out in the open: Anna's ended the shadow life she's been living since she turned her back on society, and Levin has realized how he should be conducting himself. In the wake of Anna's death, Vronsky seeks his own oblivion as a soldier in a pointless war with the Ottoman Empire.
Levin: Levin, for his part, feels at last that he truly loves his son and his wife. (He realizes how much he cares about them when he thinks they might have been killed in a lightning storm immediately after his epiphany). He knows he's still going to be short-tempered and difficult, because that's the kind of guy he is, but his bouts of anger aren't going to matter as much. He's found the meaning of life: to live for good in his little corner of the world.