In 1930s London, John Beaver is an unemployed 25-year-old Oxford graduate living at home with his mother, Mrs. Beaver. John is a charmless and unimpressive young lad, who spends his days looking to score a free lunch from among the London socialite crowd whose ranks he is eager to ascend. Widely regarded as a social climber and pest, John is nonetheless tolerated at gatherings when more desirable guests can’t be found. Mrs. Beaver is a ruthless interior decorator who keenly assists her son’s lackluster social climbing efforts. John has fastened onto a passing and insincere invite from Tony Last to Hetton, his country estate, for the weekend, and he intentionally telegrams of his imminent arrival with too little time for the invite to be revoked.
At Hetton, Tony Last surveys the deteriorating neo-Gothic décor of his beloved ancestral home, and he and his slightly younger wife Brenda Last read the morning mail. Tony dismisses all social invites they receive, preferring never to leave Hetton or host guests, despite Brenda’s desire for company. Their young son John Andrew learns horse jumping from the stable master Ben Hacket, whom the boy loves but whose gruff influence on the child disturbs his prim nanny. Being a member of the landed gentry, Tony lives comfortably on passive income and passes his time in the same small circuit of local routines, like going to church—despite his lack of interest in religion. The sudden news of Beaver’s arrival horrifies Tony, who knows him only in passing as a freeloading pest, and he plans to make Beaver’s stay as uncomfortable as possible to ensure his quick departure. When he arrives, Brenda steps up to entertain him while Tony flees to various chores. To her surprise, she and Beaver hit it off and have a nice weekend apart from the awkwardness Tony imposes. Brenda relishes hearing updates from Beaver on London gossip and her old socialite crowd. After Tony gives Beaver a proud tour of Hetton, Brenda admits to Beaver that she detests the house but hides her feelings from Tony.
On a day trip to her sister Marjorie’s in London, Brenda admits that she’s romantically interested in Beaver. Running into him again while discussing the rental of a London flat from Mrs. Beaver, Brenda eventually convinces Beaver to escort her to Polly Cockpurse’s upcoming party, a major social event. Beaver successfully kisses Brenda on the way to the party. Their dalliance has already become the talk of the town the next day, and it soon becomes a real affair. Beaver enjoys increased social clout from the affair, which his mother strongly endorses, while Brenda annoys Tony and disappoints John Andrew by returning days late to Hetton. She promptly goes to work wearing down Tony to agree to rent her one of Mrs. Beaver’s London flats. He caves in, and soon Brenda is telephoning him from the flat to gush about it while John Beaver lies beside her in bed. Over Christmas, Tony’s poorer relatives, the family of Richard Last, come to visit Hetton and discomfit Brenda with their earthy ways. Brenda fears Beaver has lost interest in her. Tony unexpectedly accompanies her to a friend’s house over New Year’s, and Beaver is also a guest there. He and Brenda intentionally steer clear of each other, but Brenda then tells Tony she will start economics courses as a pretext to spend more time in London.
Tony goes to London one evening to surprise Brenda, but she can’t be reached. He runs into his old friend Jock Grant-Menzies, who has also been stood up. The two drink heavily together as Tony becomes morose about Brenda’s increasing absence from Hetton. They go on a drunken spree, and Tony makes several drunken phone calls to Brenda’s flat, where Beaver is with her. Jock, who knows about the affair like the rest of London, helps divert Tony. Tony’s hungover shame the next day allows Brenda to become more flagrant in her disrespect for Tony: she invites Polly and other ruthless friends to Hetton, where they mock the house and Tony’s dull habits. Fearing that she’s gone too far, Brenda attempts to arrange for her apartment neighbor Jenny Abdul Akbar, a crass American widow, to seduce Tony and take the pressure off her own affair. Tony despises Jenny and her visit to Hetton fails spectacularly, though John Andrew does fancy her.
The day of the annual Hetton fox hunt arrives, eagerly awaited by John Andrew, who is reluctantly permitted to ride along. Jock and his austere girlfriend Mrs. Rattery join the hunting party. During a minor traffic jam, the villager Miss Ripon’s unruly horse kicks and instantly kills John Andrew. Jock volunteers to deliver the news to Brenda, who skipped the hunt for a party in London, while Mrs. Rattery stays to keep company with the quietly distraught Tony. She and Tony play cards to distract him while Jock tracks Brenda down to a fortune-telling party at Polly’s. Brenda at first can’t process Jock’s news, but when she realizes that John Andrew and not John Beaver was the one who died, she blurts out “Oh thank God,” later claiming that she was delirious when she said it. Brenda returns to Hetton, where Tony is ordering affairs, but she quickly leaves again to a friend’s for the weekend, where Beaver is. She declares her love for Beaver, and telegrams Tony the same, saying she will not return to Hetton. Tony is stupefied, and Jock must reveal that everyone but Tony has known about the affair.
Tony spends a few weeks at Jock’s as he processes the shock. Intermediaries inform him of Brenda’s satisfaction with the fair sum of 500 pounds annual alimony, but due to divorce laws of the time, Tony must collect “evidence” of his own adultery for the split to proceed. He arranges a weekend at Brighton, a seaside resort, with Milly, a prostitute he and Jock met during their drunken night out. Detectives follow him to collect staged “evidence,” but Milly unexpectedly brings along her horrible young daughter Winnie, threatening the whole conceit. The weekend is awkward. Back in London, Brenda’s brother Reggie meets with Tony and reveals that with this new evidence, she will in fact demand 2000 pounds alimony. Shocked and disillusioned, Tony recalls that Winnie’s presence voids the alleged evidence and counters that he will give Brenda nothing. Brenda’s friends are shocked by the news.
Feeling he needs a break from Hetton in the wake of the recent upheavals, Tony spontaneously joins the eccentric explorer Dr. Messinger’s voyage seeking a lost city in the Amazon. Onboard the transatlantic crossing, he sparks up a romance with a young, mysterious Trinidadian girl, Therese de Vitre. Tony’s offhand mention of his marriage sours the affair, and she soon disembarks. Arriving in South America, he and Dr. Messinger assemble supplies and start upstream, with Tony increasingly harried by the harsh jungle environment. They reach an Indian village, where the English-speaking Rosa acts as interpreter and helps them organize a team of Indians to guide their quest for the city. They travel inland for weeks, getting progressively more lost in the jungle. The natives build canoes for Dr. Messinger but refuse to accompany them any further, and Messinger’s incompetent negotiations scare them away, leaving him and Tony alone. After a few days of downstream drifting, Tony gets a violent fever and begins hallucinating Brenda’s presence. Messinger leaves him on shore and rows on in search of help, but he dies in a waterfall. Totally alone, Tony’s hallucinations overtake him in a terrifying blend of random incidents from earlier in the novel. Meanwhile, back in London, Brenda and Beaver’s relationship sours as her money dries up; Beaver leaves her to go to California with his mother, and her friends abandon her.
Still delirious, Tony stumbles onto the remote jungle ranch of Mr. Todd, a mixed-race English-speaking son of a missionary. Mr. Todd nurses Tony back to health, but his care soon turns sinister: Mr. Todd loves the works of Dickens that line his walls, but he can’t read, so he forces Tony to read to him endlessly—as he did to a previous visitor, whose grave is on the ranch. After several months, a search party comes looking for Tony, but Mr. Todd drugs Tony during their arrival and convinces them that Tony has died. Tony awakes, horrified at his last lifeline being severed and at his fate of having to read Dickens aloud forever.
With Tony presumed dead, Richard Last and his family have inherited Hetton, being Tony’s closest relatives. They have economized by closing several wings, laying off staff, and introducing fox farming. After a dedication ceremony for a monument to Tony, Richard’s son Teddy goes to tend to his foxes, whom he proudly views as the means to restore Hetton to its glory days as under his cousin Tony.