This plot is simple but effective. The characters are a dysfunctional couple. She poisons him to escape his tyrannical marriage, but he defends her in court and, much to her chagrin, "wins her back," in a way, which is what the novel is really about. This is a story about a kind of slavery, the male imposition of his will onto his wife, and it is about the chronic ways he does this without ever addressing the fact that although he demands a good performance of his wife, he has failed in every imaginable role he might have filled.
Look for instance at the historical idea that men are responsible for provision. The novelist offers a different picture—a man who drags his wife to the middle of nowhere, where no provision is easily attainable, where she will depend on him. Then, he feeds her only wine and cigarettes—not exactly the breakfast of champions. She feels like a servant in her own family, like a trapped rodent in a maze. She feels that her autonomy and freedom have been compromised.
In a way, therefore, this novel is not just about this specific dysfunction. Rather it is about the sad reality of many marriages, where wrongful ideas about gender role are enforced in the home, either because of power dynamic issues (an incompetent spouse enforcing their tyrannical rule by force) or because of isolation (because the husband knows he is doing something ethically wrong, but he is unable or unwilling to stop, so instead he takes her to where no one will notice how terrible of a husband he is to this poor lady).
This is clearly evident from the "Deus ex machina," his sister Anne, whose presence in the story is also a signifier that he should know better, because he has a sister in his own family, but for some reason, he views her one way and his wife another way. Perhaps this is because he knows Anne is family, but his wife he thinks of as a slave of some sort. It never occurs to him that his wife is his family too.
