Plot summary

The story dates to 1865 and is set in rural England. Katherine is married to Alexander. They live at Alexander's father's country estate. Alexander's father, Boris is a wealthy landed gentry. Relations between Katherine and Alexander are non-existent with Alexander's sexual interest in his wife is limited just to watch her naked while masturbating. Katherine's movements are limited to the house and she is forbidden from leaving the premises though she likes to go out into the countryside for some fresh air. These circumstances cause Katherine to be frustrated and bored.One day, Alexander has to leave to attend to an emergency because there was and explosion at one of their colliery at Amble. Also, Boris has to leave for London to attend to another business matter. This causes Katherine to be left alone with her maid Anna. Katherine uses this new found freedom to explore the countryside alone.One day, Katherine hears a commotion from the stable and goes to investigate. There she finds Anna wrapped up in a weighing sack and lifted above the ground. The groomsmen were laughing and one, clearly drunk, tells Anna they were weighing a sow. Katherine angrily tells them to shut up and face the wall, then release Anna, who is shown to be undressed and runs out of the room with her clothes. The drunk groomsman tries to lift Katherine to weigh her as well and she knocks him down, then warns all the men they've wasted her husband's resources and she'll be watching them from then on. When she returns inside, she asks Anna who the rude groomsman was and Anna tells her his name is Sebastian and he's new.Sebastian is attracted to Katherine and visits her in her bedchamber one night. After initially resisting his advances, Katherine and Sebastian being an affair. Their affair is discovered by Anna who informs the local priest. The priest tries to warn Katherine but she sends him away. When Boris returns, he is informed of the affair. He beats up Sebastian and locks him up and threatens Katherine when she demands his release. Katherine poisons Boris's food and calmly talks to Anna while Boris is choking in the next room.Katherine releases Sebastian and they resume their affair. Boris is buried without suspicion and Anna is terrified into muteness. Alexander informs her that he will not be returning for his father's funeral. Katherine now takes over the day to day running of the estate. One night when Katherine and Sebastian are asleep in her bedchamber, her husband Alexander returns home unannounced. She hides Sebastian in one of the adjoining rooms. After he reveals that he is aware of her infidelity, she summons Sebastian and begins to defiantly kiss him in front of her husband. A fight ensues, at the end of which Katherine kills Alexander. They then bury Alexander in the woods and kill his horse. Alexander is reported as missing but no one suspects the couple. Sebastian expresses regret for killing Alexander but Katherine convinces him that it was necessary.One day, a woman arrives at the house with a young boy named Teddy claiming that he was the result of an affair between Alexander and her daughter. She says that Alexander had accepted the boy as his ward and there were papers to prove it. Katherine reluctantly shelters the pair in the house. But this upsets the living arrangements between Sebastian and Katherine and Sebastian has to return back to living in the stable. This makes him angry. Katherine realizes she is pregnant, but is unable to inform Sebastian as he pushes her away.Katherine starts to bond with the boy Teddy. One day while trying to follow Sebastian, Katherine scolds Teddy who was trying to get her attention and grabbing onto her dress. Later, a maid tells Katherine they can't find Teddy. The household organizes a search party and Sebastian finds Teddy sitting near a waterfall and manages to bring him back. When Teddy's grandmother scolds him for entering the house as a stranger and banishes him from the house, he stalks out to the barn and tells Katherine he's tired of being humiliated and is leaving. She manages to dissuade him from leaving saying that she has a plan.When Teddy's grandmother goes to sleep, Katherine lets Sebastian into Teddy's room and they smother Teddy in his sleep. Afterwards, Katherine is shown sitting up near the coach until morning light comes in, looking unhappy and wiping her face as Anna comes in and realizes something's wrong. Katherine asks Sebastian to hide in the woods and she gives the testimony that Teddy died in his sleep. The village doctor is skeptical as he notices some bruises but Katherine claims that those were from the waterfall incident. While the issue is being discussed a guilt-ridden Sebastian enters and confesses to killing the body along with Katherine. Katherine uses this opportunity to turn the tables on Sebastian accusing him and Anna of killing Teddy, Alexander and Boris. Her word is taken over his, especially when Anna remains mute. Sebastian and Anna are taken away by the police. One by one, all the members of the household leave and Katherine remains alone in the house with her unborn child.