The aristocratic Tony Last (yes, the "last" of the Mohicans, living at the end of our civilization) is devoted to his ugly neo-Gothic homestead Hetton, to his wife Brenda and his young son John Andrew. At the start of the novel, everything seems pure happiness. But Brenda is bored with life in the country and her predictable husband.
Then a self-interested social climber, John Beaver, invites himself to Hetton and although he is childish and vapid, Brenda starts an affair with him. Yearning for urban excitement she has Tony rent her a small apartment in London and pretending to be busy studying economics, spends her weeks jet-setting with John. This is Brenda's caprice and she is so inundated in her new life that she spends less and less time with her family. Then her young son John Andrew dies from a horse riding accident. When she gets the news that "John is dead," she first thinks it is her lover... then realizing it is her son, utters one short sentence: "Thank God."
Brenda now decides she wants a divorce. These are the 1930s when divorce was not as easy as it is today. To save Brenda from a scandal, Tony agrees to take the blame and therefore has to spend a weekend in Brighton with a fake mistress - one of the most funny scenes in the book. But their agreement on the divorce falls apart when Brenda and her family insist on a monetary settlement so large that Tony would have to sell Hetton. That is the last thing he would ever do.
Now, on a caprice of his own, he leaves for South-America where he joins the expedition of a mad explorer, Dr Messinger, to find a lost city in the jungle. Everything goes wrong, Dr Messinger dies in a canoe accident and Tony falls seriously ill. He is miraculously saved by a Mr Todd ("Tod" is German for "death") who has lived for sixty years in the jungle. Todd refuses to let Tony go and - not being literate himself - has Tony read him aloud the novels of Dickens. That is how Tony will spend the rest of his life. Culture in the jungle, you may think, but it should be noted that Waugh disliked Dickens.
Brenda, in the meantime, is far from the rich divorcee that John Beaver had expected, so he leaves her in the lurch. Shortly after Tony is declared dead, she marries a mutual friend. At the end of the novel obscure relatives of Tony take over Hetton.
That is how lives go to seed when people are cold and selfish. The novel has also been interpreted as symbolical of the end of the British empire, an end due to society losing its moral bearings.
But Evelyn Waugh serves up his "message" with tons of humor in this comedy of manners and that is a good thing. Dark as the book is, it is also wildly funny - Tony's visit to a club of ill-repute, Brenda's efforts to hook him up with one of her girlfriends, or a lady called "Cockpurse" - Waugh is like Wodehouse but then on a literary higher level. Waugh also writes in a perfect style, precise and concise. In short, this is a great book.