At a country fair near Casterbridge, Wessex, a young hay-trusser named Michael Henchard overindulges in rum-laced furmity and quarrels with his wife, Susan. He decides to auction off his wife and baby daughter, Elizabeth-Jane, to a sailor, Mr. Newson, for five guineas. Once sober the next day, he is too late to recover his family. When he realises that his wife and daughter are gone, probably for good, he swears not to touch liquor again for as many years as he has lived so far (21).
Eighteen years later, Henchard, now a successful grain merchant, is the eponymous Mayor of Casterbridge, known for his staunch sobriety.
All these years, Henchard has kept the details surrounding the "loss" of his wife a secret. The people in Casterbridge believe he is a widower, although he never explicitly says that his first wife died. He lies by omission instead, allowing other people to believe something false. Over time he finds it convenient to believe Susan probably is dead. While travelling to the island of Jersey on business, Henchard falls in love with a young woman named Lucette Le Sueur, who nurses him back to health after an illness. The book implies that Lucette (Lucetta, in English) and Henchard have a sexual relationship, and Lucetta's reputation is ruined by her association with Henchard. The latter returns to Casterbridge, leaving Lucetta to face the social consequences of their fling.
To rejoin polite society Lucetta would have to marry him, but there is an obvious problem: Henchard is already technically married. Although Henchard never told Lucetta exactly how he "lost" his wife to begin with, he does tell her he has a wife who "is dead probably dead, but who may return". Besotted, Lucetta develops a relationship with him despite the risk. Yet just as Henchard is about to send for Lucetta, Susan unexpectedly appears in Casterbridge with her daughter, Elizabeth-Jane, who is now fully grown. The pair are very poor. Newson appears to have been lost at sea, and without means to earn an income Susan is looking to Henchard again. Susan, who is not a very intelligent or sophisticated woman, believed for a long time that her "marriage" to Newson was perfectly legitimate. Only recently, just before Newson's disappearance, had Susan begun to question whether or not she was still legally married to Henchard.
Just as Susan and Elizabeth-Jane arrive in town, a tidy Scotsman, Donald Farfrae, is passing through on his way to America. The energetic, amiable Farfrae happens to be in Henchard's line of work. He has experience as a grain and corn merchant, and is on the cutting edge of agricultural science. He befriends Henchard and helps him out of a bad financial situation by giving him some timely advice. Henchard persuades him to stay and offers him a job as his corn factor, rudely dismissing a man named Jopp to whom he had already offered the job. Hiring Farfrae is a stroke of business genius for Henchard, who although hardworking is not well educated. Henchard also makes Farfrae a close friend and confides in him about his history and personal life.
Henchard is also reunited with Susan and the fully grown Elizabeth-Jane. To preserve appearances, Henchard sets Susan and Elizabeth-Jane up in a nearby house. He pretends to court Susan, and marries her. Both Henchard and Elizabeth-Jane's mother keep their history from their daughter. Henchard also keeps Lucetta a secret. He writes to her, informing her that their marriage is off. Lucetta is devastated and asks for the return of her letters. Henchard attempts to return them, but Lucetta misses the appointment owing to a family emergency that is not explained until later in the book.
The return of his wife and daughter sets in motion a decline in Henchard's fortunes. Yet Susan and Elizabeth-Jane are not the root cause of Henchard's fall. His relationship with Farfrae deteriorates gradually as Farfrae becomes more popular than Henchard. Henchard feels threatened by Farfrae, particularly when Elizabeth-Jane starts to fall in love with him.
The competition between Donald Farfrae and Henchard grows. Eventually they part company and Farfrae sets himself up as an independent hay and corn merchant. The rivalry and resentment for the most part is one-sided, and Farfrae conducts himself with scrupulous honesty and fair dealing. Henchard meanwhile makes increasingly aggressive, risky business decisions that put him in financial danger. The business rivalry leads to Henchard's standing in the way of a marriage between Donald and Elizabeth-Jane, until after Susan's death, at which point Henchard learns he is not Elizabeth-Jane's father, and he realises that if she marries Farfrae, he will be rid of her. The Elizabeth-Jane he auctioned off died in infancy; this second Elizabeth-Jane is Newson's daughter. He learns this secret, however, after Susan's death when he reads a letter which Susan, on her deathbed, marked to be opened only after Elizabeth-Jane's marriage. Henchard conceals the secret from Elizabeth-Jane, but grows cold and cruel towards her.
In the meantime, Henchard's former mistress, Lucetta, arrives from Jersey and purchases a house in Casterbridge. She has inherited money from a wealthy relative who died; in fact, it was this relative's death that had kept her from picking up her letters from Henchard. Initially she wants to pick up her relationship with him where it left off, but propriety requires that they wait a while. She takes Elizabeth-Jane into her household as a companion, thinking it will give Henchard an excuse to come to visit, but the plan backfires because of Henchard's hatred of Elizabeth-Jane. She also learns a little bit more about Henchard, specifically, the details of how he sold his first wife become public knowledge when the furmity vendor who witnessed the sale makes the story public. Henchard does not deny the story, but when Lucetta hears a little bit more about what kind of man Henchard really is, she stops rationalising his conduct in terms of what she wants to believe. For the first time, she starts to see him more clearly, and she no longer particularly likes what she sees.
Donald Farfrae, who visits Lucetta's house to see Elizabeth-Jane and who becomes completely distracted by Lucetta, has no idea that Lucetta is the mysterious woman who was informally engaged to Henchard. Since Henchard is such a reluctant and secretive suitor who in no way reveals his attachment to Lucetta to anybody, Lucetta starts to question whether her engagement to Henchard is valid. She, too, is lying about her past: she claims to be from Bath, not Jersey, and she has taken the surname of her wealthy relative. Yet she came to Casterbridge seeking Henchard, and sent him letters after Susan's death indicating that she wanted to resume and legitimise the relationship. Although initially reluctant, he gradually realises that he wants to marry Lucetta, particularly since he is having financial trouble due to some speculations having gone bad. Lenders are unwilling to extend credit to him, and he believes that they would extend credit if they at least believed he was about to be married to a wealthy woman. Frustrated by her stalling, Henchard bullies Lucetta into agreeing to marry him. But by this point she is in love with Farfrae. The two run away one weekend and get married, and Lucetta does not have the nerve to tell Henchard until well after the fact. Henchard's credit collapses, he becomes bankrupt, and he sells all his personal possessions to pay creditors.
As Henchard's fortunes decline, Farfrae's rise. He buys Henchard's old business and employs Henchard as a journeyman. Farfrae is always trying to help the man who helped him get started, whom he still regards as a friend and a former mentor. He does not realise Henchard is his enemy, even though the town council and Elizabeth-Jane both warn him.
Lucetta, feeling safe and comfortable in her marriage with Farfrae, keeps her former relationship with Henchard a secret. This secret is revealed when Henchard foolishly lets his enemy Jopp deliver Lucetta's old love letters. Jopp makes the secret public and the townspeople publicly shame Henchard and Lucetta in a charivari. Lucetta, who by this point is pregnant, dies of an epileptic seizure.
When Newson, Elizabeth-Jane's biological father, returns, Henchard is afraid of losing her companionship and tells Newson she is dead. Henchard is once again impoverished, and, as soon as the twenty-first year of his oath is up, he starts drinking again. By the time Elizabeth-Jane, who months later is married to Donald Farfrae and reunited with Newson, goes looking for Henchard to forgive him, he has died and left a will requesting no funeral
"That Elizabeth-Jane Farfrae be not told of my death, or made to grieve on account of me. "& that I be not bury'd in consecrated ground. "& that no sexton be asked to toll the bell. "& that nobody is wished to see my dead body. "& that no mourners walk behind me at my funeral. "& that no flowers be planted on my grave, "& that no man remember me. "To this I put my name.