Across Egdon Heath (a "vast tract of unenclosed wild . . . a somber, windswept stretch of brown hills and valleys, virtually treeless, covered in briars and thorn bushes"), an older man makes his way. Soon he encounters a horse-drawn van, being led by Diggory Venn, a reddleman (seller of a reddish powdery dye used by sheep farmers to identify their flock). In the van is a young woman whose identity Venn rudely conceals from the elderly hiker. As he continues walking alongside the van, the reddleman notices the figure of a woman, standing atop Rainbarrow, the largest of the many Celtic burial mounds in the area, profiled against the sky, "like an organic part of the entire motionless structure," and then, replacing her, other figures. These are heath folk (locals, living near the heath) come to start a Fifth-of-November bonfire, a local custom. The night sky is lit by a number of these bonfires.
The young woman traveling in Diggory Venn's horse cart is Thomasin Yeobright, who was to have married Damon Wildeve that day. Mrs. Yeobright takes Thomasin with her to see Wildeve at the inn he operates in order to demand an explanation of his failure to marry her. When their bonfire has burned out, the locals come to serenade Thomasin and Wildeve, thinking them to be newly married and wanting to celebrate. When Wildeve is able to get rid of them he starts off to see Eustacia Vye, the mysterious figure Venn saw earlier, standing on Rainbarrow.
Eustacia watches for Wildeve on Rainbarrow, returning now and then to check on the signal fire she has had built before her grandfather's house. (Captain Vye is the chance acquaintance of Venn's). Wildeve was once Eustacia's lover, but she has not seen him since his interest in Thomasin. Eventually, Wildeve does finally arrive.
Venn accidentally learns of the meeting between Eustacia and Wildeve. A longtime admirer and once rejected suitor of Thomasin, Venn thinks he can score points with her. He now resolves to help her and purposely overhears the conversation between Eustacia and Wildeve the next time they meet on Rainbarrow. Venn then calls on Eustacia to get her to help Thomasin, finally telling her he knows about her meetings with Wildeve. Venn also informs Mrs. Yeobright he would like to marry her niece. Though he is rejected, the aunt uses him as a means to put pressure on Wildeve. Wildeve goes immediately to Eustacia to convince her to leave with him, but she will not answer right away.
The news of the arrival for the Christmas holidays of Mrs. Yeobright's son, Clym, is widely talked about on the heath, including Captain Vye's house, where Eustacia also hears about his impending visit.
Mrs. Yeobright and Thomasin make preparations for Clym's arrival. After getting a glimpse of him, Eustacia is fascinated by him. She arranges to substitute for one of the boys in the traditional Christmas mumming (a play or pageant in which the actors use gestures, masks, props, and elaborate makeup, but do not have spoken lines), the first performance of which is at a party Mrs. Yeobright is giving. During the performance at the party, Eustacia succeeds in meeting Clym while she is in costume. Now that her interest in Wildeve has paled, Eustacia makes clear to Venn that she would like to see Wildeve married to Thomasin. They do marry, with Eustacia serving as witness. Mrs. Yeobright, who has once opposed the marriage, does not attend; and Clym, who has been away from home, finds out about the marriage after it has taken place.
Giving up his business career in Paris, Clym has returned to Egdon Heath to set up as a schoolteacher to those who can't afford existing schools. Mrs. Yeobright disapproves, thinking Clym's career goals do not show enough ambition. Clym meets Eustacia, in her own person this time, and is strongly attracted to her, an attraction that Mrs. Yeobright argues against. Clym sees Eustacia regularly, usually on the heath, for several months and then asks her to marry him. She says yes, though she hopes he will finally give up his plans and take her to Paris.
When Mrs. Yeobright and Clym quarrel over his love of Eustacia and he feels forced to leave his mother's house, he decides he and Eustacia should marry right away and live for a time on the heath. Clym finds a cottage and moves from home, leaving his mother disconsolate and bitter. Wildeve's interest in Eustacia revives when he hears of her approaching marriage.
On the occasion of their marriage, Mrs. Yeobright decides to send a gift of money. Her son, Clym, is marrying Eustacia against her wishes, and she hopes that, by offering this gift, she and her son can repair their relationship. The other half of the money is to go to her niece, Thomasin, who has recently married Damon Wildeve, Eustacia's former lover. Unfortunately, Mrs. Yeobright selects as her messenger the inept Christian Cantle, the village simpleton. Cantle loses the money gambling with Wildeve, who wants revenge on his wife's aunt for not trusting him with the money. Venn, protecting Thomasin, wins it back from Wildeve, but not understanding that part of it should go to Clym, Venn he delivers it all to Thomasin.
Eustacia and Clym for a time live a secluded life. When Mrs. Yeobright receives no response from Clym about the money, she calls on Eustacia, and they quarrel bitterly. Clym, hurrying his study to be a teacher so as to pacify the impatient Eustacia, develops severe eye trouble and is forced to suspend his work. To his wife's dismay, he takes up furze cutting (furze is a low, prickly shrub) as a way of making a little money and getting exercise. To Eustacia, this is a far cry from what she yearns for — the gay life of the great world, especially as represented by Paris — and since Clym had business and connections in Paris, Eustacia saw him as a way out of her constrained life on the heath. To compensate, she goes to a gipsying (a dance) and unexpectedly encounters Wildeve and dances with him. Venn sees them together and attempts to discourage Wildeve's loitering around Clym's house at night.
Persuaded by Venn to forget her pride and call on her son, Mrs. Yeobright starts the long walk to his house on a hot August day. She sees Wildeve admitted by Eustacia before she can get there; when she knocks on the door, Clym's wife looks out the window but doesn't answer. The older woman tries to walk back home, stops in exhaustion, and is bitten by an adder. She is later discovered by Clym, who has set off for her house to attempt a reconciliation, but even medical attention cannot save her and she dies. Clym blames himself for her death. Eustacia is nearby when Mrs. Yeobright dies but doesn't make an appearance; she has accidentally encountered Wildeve, who has lately come into an inheritance.
Clym for some time is ill and irrational because of his mother's death. His constant blaming of himself exhausts Eustacia, and she tries to find consolation in Wildeve. Once back to normal again, Clym sets out to discover what his mother was doing on the heath. From Mrs. Yeobright's handyman, Cantle, from Venn, and a young boy who came across his mother as she tried to get home that day, Clym learns what happened. He accuses Eustacia of cruelty to his mother. When Clym adds the charge of deception of himself as a husband, the relationship between him and Eustacia is effectively over. She leaves his house to return to Captain Vye's.
At her grandfather's, Eustacia doesn't know how to occupy herself and once even thinks of suicide. A bonfire is lit for her when the Fifth of November comes, an inadvertent signal to Wildeve, who offers to help Eustacia get away from the heath to Paris. On Thomasin's advice, Clym, now moved back to his mother's house, writes to ask his wife to return to him.
On the evening of the sixth of November, Eustacia signals to Wildeve that she wants to go, by chance not getting Clym's letter before she leaves the house. Thomasin, has suspicions about Wildeve. She and Captain Vye, who finds out Eustacia has left the house very late at night, come to ask Clym's help. Thomasin tries to get back home, finally with Venn's assistance. While Wildeve waits with a horse cart for Eustacia, and Clym searches for his wife, Eustacia on this dark, stormy night throws herself in a stream near a weir. Both Wildeve and Clym try to rescue her, but it is Venn who pulls out both men as well as Eustacia. Of the three, only Clym survives.
After her husband's death, Thomasin moves into the family home with Clym. Venn, having given up the reddle trade, calls on her, and they become interested in each other. However, Clym thinks he ought to ask his cousin to marry him since his mother wished it. But Thomasin and Venn decide to marry and do. Clym is last seen on top of Rainbarrow, performing as an itinerant preacher of moral lectures.