It is threshing day at Flintcomb-Ash, and all the women gather around the sinister red threshing-machine. Nearby is a black, smoking engine, tended to by an engineer who serves its fire and industry and looks out of place in nature. He is strange and Northern and seems like a servant of Hell.
Hardy is at his most explicit here in portraying modern industry as Hellish and destructive, a fiery intrusion on Nature. The engineer seems similar to the eerie Arctic birds.
The women start to work, feeding the ravenous machine with corn. Old men talk of the hand-labor of the old days, which got better results. Tess does not even have time to talk, she must work so fast to satisfy the machine.
Hardy empathizes with the old men in his nostalgia for the agricultural past. The machine is never satisfied, and the work becomes unbearable for the innocent, rural women.
Tess doesn't notice that Alec d'Urberville has arrived and is watching her. He is dressed fashionably now, no longer like a preacher, and Izz and Marian can't believe he is the same man. Tess takes a break and is surprised to see him. It is clear from his appearance that he has returned to his old libertine ways.
Alec has totally reverted to his original ways. Tess doesn't even have his own shame protecting her from his advances now. He also comes upon at her at her weakest, when she is made vulnerable by the terrible machine.
Tess asks why he keeps bothering her, but Alec accuses her of bothering him by haunting him with her eyes and ruining his faith. He has entirely given up religion, and blames Tess for taking his innocence as revenge for him taking hers. He says no saint could have kept the faith either if tempted by her face.
Alec admits that Angel's arguments have convinced him, and Tess asks that he keep the religion of kindness and purity, if not doctrine. But Alec says if he has no one telling him what to do then he will do what feels good – he has no inner moral compass.
Tess's religion is clarified as the morality behind Christianity without the dogma. Alec doesn't have the capacity to live in this way without acting reckless.
Alec emphasizes how Angel has abandoned Tess, and again he propositions her, implying that he is closer to her than her mythical husband. He reaches for her and Tess slaps him in the face with her glove. Alec jumps up, bleeding from the mouth, and Tess invites him to attack her, because “once victim, always victim.”
Alec does not retaliate, but he does threaten Tess that he will be her master again, and if she belongs to anyone it is to him, not Angel. He leaves and the machine starts up again, and Tess keeps working, stunned.