The Last Train to Zona Verde, By Paul Theroux Tomorrow I'll be Twenty, By Alain Mabanckou, trans. Helen Stevenson

As a great traveller abandons hope in modern Africa, a voice from Congo refreshes the spirit

African paradise lost? A settlement along the Congo river, Republic of Congo (Alamy)

Paul Theroux never made it to the place he calls "the Congo". Disgusted by the "squalor and decrepitude" of "horror cities", he gives up his overland journey up the continent's west coast in Angola: for him, the epitome of a "futureless, dystopian, world-gone-wrong, Mad Max Africa". In what amounts to a great travel writer's professional suicide note, he claims that, to the north, "I knew what I would find: decaying cities, hungry crowds, predatory youths, people abandoned by their governments".

Well: this February, I went where Theroux feared to tread. In Brazzaville, capital of the Republic of Congo and one of his unvisited hell-holes, I heard dozens of African writers, both Anglophone and Francophone, chew over the burdens and afflictions that Theroux details, with all his brutal frankness. But they safeguarded a virtue he had lost on wheezing buses along the dusty, potholed roads: hope.

I strolled through the "shantytown" of Bacongo, by the sea-wide river, in the company of a witty and subtle Angolan novelist - José Eduardo Agualusa. (Theroux wrongly dismisses Angolan literature as "humourless, self-righteous and provincial".) We tracked down a couple of the famous "Sapeurs" who defy the surrounding hardship with displays of designer-label peacock finery, and replied to the "bonsoirs" of well-mannered kids. There were lots of schools.

I owed the gift of Brazzaville to the versatile and charismatic Congolese writer Alain Mabanckou, prime mover behind the country's first arts and literature festival. If you choose to join Theroux's apocalyptic and despairing drive from Cape Town to Luanda, then turn for a respite to the clear-eyed warmth and charm of Mabanckou's semi-autobiographical novel about a childhood in Pointe-Noire - Congo's port. It will cleanse the palate, and refresh the spirit.

Africa's future matters too much for propaganda and special pleading. Congo-Brazzaville, the gods know, faces problems enough. Still, in the former French colony we could do what remains quite inconceivable across the vast river in the war-ravaged Democratic Republic of Congo - first Belgium's abused treasure-chest, and now a mineral-hungry planet's. Shameless kleptocrats in power; the hypocrisy of foreign aid (Theroux's scorned "virtue industry"); the grotesque theft of resources by tiny elites in cahoots with Western - and now Chinese - corporations; the flight from village life into (Theroux again) "the blight of incomplete and misdirected modernity": these realities deserve no evasions or euphemisms. Michel, Mabanckou's sweet-natured and forever curious 10-year-old narrator, accepts almost as a fact of nature that "the finance minister is someone who steals the country's money".

Theroux himself argues that "Colonialism oppressed and subverted Africans and remade them as scavengers, pleaders, and servants" - the literary pioneers of négritude said as much almost a century ago - and that "colonial-mimicry", post-independence, has just repeated that pattern.

However, The Last Train to Zona Verde - a "symmetrical" west-coast journey to match his east-coast Dark Star Safari (2002) - ends up by doing a huge favour to the uniformed local embezzlers, the besuited foreign plunderers and the "parachuting pop stars" (Bono and Madonna take a merited pasting). They may dismiss its more justifiable outbursts of indignation as merely a bitter old man's pain.

Theroux's "valedictory trip", his farewell to a genre of rough travel that once promised "bliss", treats the urban Africa he loathes as the outward sign of an inner disillusion. Feeling ancient (a septuagenarian backpacker), vulnerable, world-weary, he makes of Africa's shift from the "mutual respect and fairness" of rural tradition to "stupefying disorder" in the cities a corollary of his own sense of doom. He knows the idea of Africa as a "violated Eden" is an outsider's myth. Indeed, a fine chapter sets the "charade" and "travesty" of life among the heritage-industry San people today against the fantasies of pristine innocence spun by "posturing fantasists" such as Laurens van der Post. Travellers in Africa always see the continent through the "distorting mirror" of their dreams and fears. Too true.

Yet, among the tourist-packaged Ju'/hoansi ("Real People"), he can't let go of that hunger for purity. Later, he converts his journey - more in detested Angola than "brighter and better" South Africa or Namibia - into a dark night of the ageing soul. The opening chapters, on a township tour in Cape Town or a luxury elephant-back safari in Namibia, offer excellent, barbed reportage à la Theroux: ironic, sceptical but still avid for news. Then the book falls off an emotional cliff. Granted, the peculiar depths of oil-rich Angola's corruption and inequity do offer a fitting backdrop for a "doomsday vision".

He seems to stop watching and listening in the way that has always fed his prose. The shutters come down: "every city is the same... a perfect fright". Angolan high spirits reflect "hysteria" - "a shrieking, chaotic... society on the brink of extinction". Contrast Mabanckou's Michel (his voice translated with grace and brio by Helen Stevenson), who learns with sad concern that because "it's so cold over there in Europe, people don't laugh much".

In a key image, Theroux sums up the dashed hopes and false choices of the African city in the form of three greasy, stringy chicken legs in a vendor's bucket - each equally repulsive, yet each unavoidable. In Tomorrow I'll be Twenty, Michel meets a rubbish-tip philosopher named Little Pepper. He spins the kid a story about how his wise and beloved grandfather's spirit entered a lone cockerel, so that now he can't see "a chicken thigh in a bin" without recalling "the man I loved more than anyone".

Still a pastoral nostalgist who pines for village life and believes like Thoreau "in the forests and the meadows", Theroux finds in the teeming cities an abbatoir for humanity, memory, affection. To Mabanckou, those qualities endure even in the discarded chicken leg of a crazy garbage-heap sifter. I suspect that his little Michel would feel sorry for the jaded, joyless voyager. And so, in the end, does the reader.