Mary is initially indifferent to Moses' presence as a houseboy, but eventually, she starts to feel a change in herself. Losing interest and attention for things outside of the house (even things that she had been responsible for before, such as taking care of the chickens), Mary falls into a kind of daze and cries frequently for reasons she cannot clearly understand. After a month of service, Moses comes to her to ask if he may leave; thinking of the arguments she would have to have with Dick over her making another houseboy leave and her confusion over what to do in the house, Mary breaks down in tears in front of Moses, which is terribly humiliating for her.
With his mistress in such a terrible state, Moses gives her a glass of water and makes her drink it; then, he commands her to lie down in bed. When she does not, he gives her a light push, this contact being the first that Mary had ever experienced with a black person. As she drifts into sleep, she feels deeply disturbed by what has happened.
After this incident, Mary feels herself to be helplessly in Moses' power. Moses, for his part, dispenses with many of the subservient practices that would normally be demanded of him, such as not speaking in English.
Mary has nightmares that replay Moses standing dominantly over her in the bed and wakes up in terror. When Dick falls ill with malaria for a second time and Mary exhausts herself taking care of him, Moses makes her take a rest while he takes over; in this sleep, Mary dreams that Moses has murdered her ill husband by opening a window and letting in a deadly chill, and then that Moses is coming threateningly towards her. She wakes up and goes to Dick's side. When her nightmares of Moses continue after Dick has gotten better, she begins to fear being left alone with the native and feels a sense of security sleeping by Dick's side. She feels locked into a dark and terrible conflict with Moses.
In the years that Mary has lived with Dick on his farm, they have, unbeknownst to themselves, furnished a great deal of gossip material for their neighboring farmers. Most of the stories, such as that of Mary's flight from the farm, come from the Slatters. Charlie Slatter is essentially fond of and somewhat avuncular towards Dick, but as a farmer whose ambitions were stoked by a sharp increase in fortunes brought on by higher crop prices during the First World War, his plans are ultimately to absorb Dick's farm into his own.
Charlie and his wife drive over to the Turners' to try to convince Dick to sell his farm to them. Charlie argues to Dick that he, Dick, is not making any money with the farm and would do far better finding a job in town; Dick, however, is unwilling to leave his land, as he does not know how he would live and make a living elsewhere. The argument reaches a standstill until Charlie notices and is profoundly disturbed by the way that Mary talks to Moses in front of them; she speaks with the same kind of familiarity, even flirtatiousness, with which she speaks to Charlie.
This violation of race divisions makes Charlie compel Dick to let Tony Marston, a young and idealistic Englishman working for Charlie, to take care of his farm for some months while Dick takes Mary to the seaside to recover. Dick reluctantly accepts, but the stress of his departure wears on his mind.
Marston is shocked to see Mary allowing Moses to dress her, and he has her fire Moses.
Lying in bed next to Dick, Mary feels that he has prevented her from living her own life. He wakes up and, worrying for her, tries to speak to her, but then he falls asleep again. In this solitude, Mary gets up and goes to the bedroom window to see the sun rising. At first, the sight fills her with a sense of liberation and fulfillment, but then the daylight plunges her into despair at being left in the same situation.
Tony Marston urges her to see a doctor. Mary says that she is ill but refuses to see a doctor. That night, after Dick and Tony have gone to bed, Mary finds herself unable to sleep, haunted by the delusion of Moses' climbing on the roof and trying to get at her. To escape this claustrophobia, she rushes into the veld, where Moses appears and, in the midst of a lightning storm, kills her with a blade. Moses considers killing Tony too and escaping, but he feels so filled with a sense of victory and satiated vengeance from having killed Mary that he instead remains on the veranda where he put Mary's body, where he will later be found.
The last three chapters of the novel effect a reversal in which Mary, who embodies white power in a declining form, finds herself dominated by Moses, the black man whom she had thought she could control with the sjambok. Although we are not granted access to Moses' private thoughts and emotions until the very end of the novel, we are able to sense through Mary's perspective both his extraordinarily strong character and the uncanny reciprocal relationship, at once sexual and racial-ideological, between the two of them. Indeed, Moses' primary function in the novel lies in the powerful foiling role that he plays to Mary's frustrations, anxieties, and desires.
While working in the field away from the domestic sphere to which Mary belongs, Moses, regardless of his character, is no threat to her. However, when he is admitted into the house as a houseboy because of his education and competence, his very presence effectively traps Mary; she cannot fire him (for she has fired too many houseboys in the past) and she cannot escape (for her one previous attempt ended in failure). He is always there in the daytime while Dick is away in the fields, and so Mary cannot help but feel split between these two male figures—the most important scene of this conflict taking place in the bedroom. As we hear in the final chapter while Mary lies next to Dick:
"She rocked herself slowly back and forth, with a dim, mindless movement, trying to sink back into that region of her mind where Dick did not exist. For it had been a choice, if one could call such an inevitable thing a choice, between Dick and the other, and Dick was destroyed long ago. ‘Poor Dick,' she said tranquilly, at last, from her recovered distance from him; and a flicker of terror touched her, an intimation of that terror which would later engulf her" (202).
This "terror," all the more terrifying for not being explicitly named, is Moses—or, more precisely, the idea of Moses as an opposite to Dick and Mary.
Unable to resolve this conflict within the household and within herself, Mary gives herself up to it. The previous chapters have shown us how she vacillates between times of great motivation and vegetating lethargy; in her relationship with Moses, Mary reaches the dark margin of madness where these two become indistinguishable in an unbearable feeling of doom:
"There was now a new relation between them. For she felt helplessly in his power. Yet there was no reason why she should. Never ceasing for one moment to be conscious of his presence about the house, or standing silently at the back against the wall in the sun, her feeling was one of a strong and irrational fear, a deep uneasiness, and even – though this she did not know, would have died rather than acknowledge – of some dark attraction" (163).