Ethan returns to the house to find that the sleigh has come to take Mattie's trunk to the station and that Zeena is in the kitchen reading a medical book. He asks where Mattie is, and Zeena replies that she is probably bringing down her trunk.
Ethan goes up to Mattie's room and finds her sobbing on the bed. He lays his hands on her shoulders and she confesses that she feared she would never see him again. He takes her in his arms and lays his lips on her hair. Zeena calls for them to hurry and bring the trunk. They lift the trunk into the sleigh. He tells Mattie that he will drive her to the train, in spite of Zeena's wish that Jotham should take her.
At dinner, Ethan cannot eat. Zeena eats heartily, and once again there is a smile on her face. Jotham asks Ethan what time he should come for Mattie. Ethan tells him not to bother, as he will drive her. Zeena protests, on the grounds that Ethan needs to mend the stove in the spare room in time for the hired girl's arrival, but Ethan overrules her.
Ethan harnesses the horse, remembering sadly the day he had made the same preparations in order to collect Mattie and bring her to the farm. When he returns to the house, he finds Mattie in his study, taking a last look around. She reports that Zeena, without saying goodbye, has gone upstairs suffering from shooting pains, and does not want to be disturbed.
Ethan and Mattie get into the sleigh. Ethan drives off, taking a long way round, so tht they can pass Shadow Pond, a place that holds happy memories for them. When they arrive at a wood where they had a picnic, Ethan stops the sleigh and they walk around the area. They sit on a log, and Ethan reminds that this is the place where he found a gold locket she had lost. He longs to touch her and speak lovingly to her, but does not know how. She rises and suggests that they move on.
Back on the road, Ethan asks Mattie about her plans. She says she will try to find work in a store. He reminds her that her health would not stand it. He tells her that he would do anything within his powers for her. She pulls out Ethan's note to Zeena, which he had abandoned and forgotten to destroy. Liberated by her broaching the subject of their being together, Ethan asks her if she would have agreed. But she declares that there is no point in thinking about it, tears up the note and throws it away. When he presses her, she admits that more than once, she had entertained the thought; the first time was at Shadow Pond.
Ethan tells her regretfully that he cannot do a thing to help their situation. She tells him he must write to her. He believes that she will marry, and says he would rather she were dead. Sobbing, she agrees.
Continuing on their journey, they come across a group of boys with sleds. Ethan reminds Mattie that they had intended to go sledding the previous night. Ethan suggests they should do it now. They find a spare sled under the Varnums' spruce trees, where he had caught up with her after the village dance (Chapter 2). She sits in the sled and he takes his place behind her. She is worried that he will not be able to see properly in the fading light, but he boasts that he could go down the slope blindfolded. They go down the slope, and Ethan skilfully steers clear of the dangerous elm at the bottom. They walk back up the hill, and at the top, Mattie asks if this is where he caught Ned Hale and Ruth Varnum kissing. She flings her arms around him and kisses him passionately, bidding him farewell. He protests that he cannot let her go. They hear the church clock strike five, but agree that neither wants to go anywhere without the other.
Then Mattie thinks of a plan that will ensure that they will never have to part. She asks Ethan to take her down the slope again and collide with the elm so that they die together. At first he dismisses the idea as crazy, but she points out that she does not want to leave him and is unable to manage on her own.
Ethan thinks of the hated vision of the home and wife he is to return to, and the joy of knowing that Mattie felt about him the same way that he felt about her. Unable to tolerate going back home to Zeena, he and Mattie take their places on the sled and he sets it in motion. The sled only needs to follow the track to collide with the elm. As the big tree looms closer, he seems to see Zeena's twisted face thrust itself between him and his goal, and the sled glides off course. He rights it again, and they hit the elm.
Ethan regains consciousness to a 'cheep' sound like a mouse in pain. Unable to tolerate the sound of a suffering animal, he feels around for the source of the sound. His hand finds Mattie's hair and face. He places his face close to hers, sees her eyes open, and hears her say his name. Then he hears his horse whinny, and remembers that he will need to be fed.
The mood of this chapter is one of mounting despair and an unescapable fate, which Ethan feels powerless to alter: "It seemed to Ethan that his heart was bound with cords which an unseen hand was tightening with every tick of the clock." This conviction of being bound, of course, absolves Ethan of responsibility for his fate. He is incapable of making a decision and following it through into action. Instead, he constantly defers to external factors and blames them for the lack of fulfilment in his life, whether they be the climate, his marriage to Zeena and the accompanying social conventions, fate, or his financial difficulties. His decision not to ask the Hales for money for a second time can be put down to moral scruples.
Some would say that moral scruples are an internal rather than an external factor, but the fact that they arise at all in this instance is due not to the ethical force of Ethan's inner nature, but to a chance meeting with Mrs Hale and the words she chanced to utter. Then Ethan had two options as to how he would act on her words, and chose the option of helpless resignation to his married fate. His sense of duty to Zeena, in turn, is forged by external conventions (duty to the spouse) rather than heartfelt devotion to her or even a sense of her deserving ability. He is convinced (as his farewell note to her revealed) that the service he has devoted to her has been of no benefit to her or to him, and only feels hatred for her.
Ethan is at least able to muster enough determination to stand up to Zeena in his insistence on on driving Mattie to the station himself. But he cannot see any alternative to going along with his wife's plan to banish Mattie. Wharton uses the metaphor of 'coasting' (sledding) to encapsulate Ethan's passive approach to life. While it is possible to steer a sled, sledding is essentially an activity dictated by gravity: you let go and end up where the slope takes you. Having got into the 'sled' of his marriage with Zeena, he seems able only to keep in the tracks established by other 'coasters' - the rest of conventional society - and resign himself to his fate. Modern usage of the word 'coasting' reinforces this metaphor: we say that someone is 'coasting' if they are moving aimlessly through life with little effort.
Mattie is emboldened by her discovery (via Ethan's note to Zeena) that he had planned to leave his wife for her. She confesses that she has loved Ethan for a long time, revealing for the first time that Ethan's feelings are fully reciprocated. This heightens the sense of impending tragedy, as there is more at stake: we know now that the two could make a real future together. But Ethan insists, "I'm tied hand and foot," seemingly leaving them no option but the extreme one they end up taking. It is Mattie who seizes the initiative in the sledding scene, thinking up the suicide pact so that she and Ethan need never be parted. Ethan at first responds to the idea with incredulity, but as he has done all along, he allows himself to be led, and gives in to Mattie's suggestion. His boast during their first coast that he could go down blindfolded has a double ironic resonance: it foreshadows their deliberate crash, and in a wider sense, it refers to Ethan's tendency not to look out for himself but to be dictated to by others. Similarly, Ethan's reflection as they walk up the hill after their first coast, that this will be the last time they will walk together, is ironic in light of the revelations of the final chapter, which tell us that Mattie never walks again.
In a terrible irony, even the suicide pact, traditionally the plan of last resort for despairing lovers, fails. Ethan and Mattie are denied their ecstatic resolution-in-death. They survive the crash, though they are terribly injured, a fact that is not yet established but that is foreshadowed by Ethan's belief that Mattie's half-conscious groans are made by a suffering small animal.