The Peruvian writer Mario Vargas Llosa carries the mixed blessing of a 2010 Nobel citation that praises him “for his cartography of structures of power and his trenchant images of the individual’s resistance, revolt and defeat”. Never mind that the same words broadly describe every episode of Fawlty Towers, they also summon up the cod liver oil view of literature: books are good for you, and their value positively correlates with their indigestibility.

In fact, Vargas Llosa’s 16th novel is as straightforward and as engaging as its hero, Felícito Yanaque, a man who wakes up one morning to find himself the target of extortionists. A note has been pinned to his door demanding protection money from his haulage business. In place of a signature is a hand-drawn spider.

The sums involved are relatively small, but while friends and family counsel compromise, Felícito refuses to give in. Short, middle-aged and unprepossessing, she has fought his way up from a hardscrabble childhood in provincial Peru, guided by a single precept from his dead father: “Never let anybody walk all over you, son.” His defiance provokes his enemies to attempt more brutal means of persuasion. Soon the stage is set for a showdown between a man of unbending principle and an implacable foe.

Who is behind the letters? Can the extortionists ever be thwarted? As the stakes rise, will Felícito yield or break? These questions propel a novel which shares some DNA with a classic thriller plot, but whose magnanimity, comedy and moral concerns make it something closer to a fable.

Felícito lives in Piura, a provincial town in north-west Peru where Vargas Llosa spent part of his childhood. It’s depicted with great fondness, from the heat of its climate to its buzzing flies and the shade of its tamarind trees. Its crowded streets are peopled with affectionately drawn minor characters – an impecunious, honest policeman named Sergeant Lituma; the soothsayer Adelaida, in her shop in the slaughterhouse district; Mr Lau, the Chinese grocer. The Piurans’ regional slang is the lone stumbling block in Edith Grossman’s otherwise smooth translation. Poor translators! Like traffic police, they tend only to get noticed when things go badly. Every now and again a Piuran character in the book will punctuate a sentence with “hey waddya think”. It’s a rendition of the slang expression “che guá”, which has no exact English equivalent. Leaving it in the original is probably against the rules of the translators’ guild, n’est-ce pas? But could “innit”, “say what”, or even “hoots mon” be any more distracting?

Felícito’s story is twinned with that of another discreet hero, with whom his life is destined to intersect. Don Rigoberto, a successful accountant in Lima who has previously appeared in Vargas Llosa’s fiction, has made some powerful enemies of his own: after agreeing to witness his elderly boss’s marriage to a much younger woman, he’s threatened by the man’s estranged hoodlum sons. As if this weren’t bad enough, a mysterious stranger called Edilberto Torres has started shadowing Don Rigoberto’s adolescent son, Fonchito. There is more than a suggestion that Edilberto may be an incarnation of the devil.

The Discreet Hero finds its characters enjoying the fruits of Peru’s economic development. Visitors from Lima are astonished to find that provincial Piura has acquired cinemas and boutiques, but the affluence has given new scope to human rapacity. Felícito and Don Rigoberto are both challenged and disappointed by a younger generation that has forsaken hard work, been seduced by materialism and mangles its Spanish. “This is the result of progress,” sniffs the policeman to whom Felícito shows the extortion note. “When Piura was a poor city, these things didn’t happen.” The book asks us not to mistake the sheen of prosperity for civilisation.

Vargas Llosa has spent a lifetime examining individuals who inhabit corrupt systems, whether it’s in the military academy of his first novel, The Time of the Hero, or the Dominican Republic under the dictator Trujillo in 2001’s The Feast of the Goat. In 1990, his political convictions drove him to take a quixotic tilt at the Peruvian presidency, running as the candidate of an alliance of conservative, pro-business parties. He’s described his own “long and difficult” journey from youthful socialism to a tentative liberalism. There’s certainly a whisper of this in The Discreet Hero, where Felícito’s fight against extortion leads to an unsuspected terminus in the human heart. The malign figure of Edilberto Torres suggests too that the source of evil lies beyond our understanding: an acknowledgment that neither humans nor the social systems they inhabit are perfectible. Don Rigoberto, who has attempted to construct a consoling reality out of the books and music he loves, decides that the predatoriness around him is “one more proof that the small spaces of civilisation would never prevail against immeasurable barbarism”.

But the reversals and betrayals of the book’s interlocking plots owe as much to telenovelas as the writings of Isaiah Berlin. The characters may feel that civilisation – real civilisation – is always threatened by malice, but the warmth and energy of the novel, and the genial presence of its author, negate the bleakness of this moral.

• Marcel Theroux’s Strange Bodies is published by Faber. To buy The Discreet Hero for £15.19 (RRP £18.99) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.