A theyyam dancer performing in Kerala

At the end of this week I will be setting off on a bus full of ganja-smoking tantric madmen from rural Bengal. Also on board will be a Keralan dancer and part-time prison warder who is widely believed to be the human incarnation of the god Vishnu; five fakir monks from the badlands of Pakistan who sing in a sort of castrati falsetto; a smoky-voiced Tamil diva who has helped to keep alive an ancient but dying sacred song tradition from the temples of southern India; and an anthropologist of Sufi mysticism who does amazing Jimi Hendrix-ish things with his guitar. It’s going to be an interesting few months: Spinal Tap on a potentially fatal collision course with the Kumbh Mela pilgrimage.

It’s all part of what will be a year-long tour to launch my new book, Nine Lives: In Search of the Sacred in Modern India. Like many other authors, my books used to be launched with a simple drinks party – the usual plastic-cups-and-a-couple-of-speeches affair, somewhere at the back of Holland Park. These days, however, there has been a radical change in the way books are launched. Behind this lies the striking growth of the whole global literary festival bandwagon.

Last month Private Eye magazine ran a cartoon showing two survivors of a shipwreck watching their liner sink from a desert island, shaded by a single drooping palm tree. One says to the other, “Well, I suppose the first thing to do is to start a literary festival.” There is a serious point here: literary festivals have proved globally contagious (I plead guilty here: I helped found the one at Jaipur in India). It seems that as we all spend more time at our screens, looking at the virtual, the allure of a real presence – of seeing and hearing a living, breathing human being – has exponentially increased.

Even modestly successful authors can expect invitations to enough literary festivals to fill all the weekends of a summer, thus almost indefinitely slowing down the painful process of getting back to work. In addition to allowing authors who might have difficulty being recognised at their local post office to be adored and feted by crowds of admiring middle-aged women, festivals also provide the wonderful illusion that by promoting your book you are at work, while, in truth, you are on holiday.

Given this, A-list writers can now increasingly be divided into two camps: there are those, such as Cormac McCarthy or Thomas Pynchon, who apparently never leave the house . At the other end of the spectrum, there are writers such as Margaret Atwood or Salman Rushdie who throw themselves into the whole global promotional thing with an almost frenzied abandon, starring at festivals and bookshop readings across several continents. Rushdie wrote a letter to The Guardian last year about how many copies he had managed to sign in a single hour in some town in the US Midwest.

In this new world, being an articulate extrovert certainly helps. Those who can speak brilliantly, funnily, and without notes, tend to sell more books, and get more invitations, than those who are shrinking violets. In the evolutionary jungle of these festivals, having a particular act or a special talent is also a great help. Louis de Bernières now tours book festivals with his collection of mandolins and a piano accompanist. He has developed a splendidly idiosyncratic singalong performance that ends with the audience joining in his rendition of old music-hall classics.

All this has led me to where I stand now: nervously poised to spend a year of my life circling the globe with a busload of saffron-clad holy men who, even in their native Bengal, are known as the Bauls, which means, simply, the madmen.

. . .

The roots of this strange roadshow lie in a trip I made to Bengal in winter 2003. I knew that around the middle of January each year, several thousand wandering minstrels meet in the flat flood plains 100 miles to the north of Calcutta for the biggest gathering of tantric musicians in the world. As night draws in, the Bauls crowd round their fires and begin the singing and frenzied dancing that will carry on until dawn.

A Baul singer

I was in Bengal to write an article on a group of three celebrated Baul singers I had previously only heard on CD. I had been told that they would be staying in a small house off the main bazaar. To get there you had to pick your way through the usual melee of Indian religious festivals: street children selling balloons and marigold garlands; a contortionist; a holy man begging for alms; a group of argumentative naked naga sadhus; a hissing snake goddess and her attendants; lines of bullock carts loaded with clay images of the goddess Durga; beggars and mendicants; and a man selling pink candy floss to a blare of Bollywood strings.

By the time I found the house, a simple unfurnished Bengali hut, it was dark and the Bauls were in full song. They had scattered straw on the ground and were sitting in a circle around the fire, cross-legged on the floor, breaking their singing only to pass some ganja or small tin cups of Old Monk rum from one to the other.

Kanai was a thin, delicate and self-possessed blind minstrel, then in his fifties, with a straggling grey beard and a pair of small cymbals in his hand. Beside him sat a handsome old man, Kanai’s great friend and travelling companion Debdas, singing with a dugi drum in one hand and an ektara, a string instrument, in the other. His hair hung loose, as did his great fan of grey beard. Facing these two was one of the other most celebrated Baul singers in Bengal. Paban Das Baul was a handsome and hyperactive figure, then in his late fifties, with full lips, a shock of wiry pepper-and-salt hair, and a short goatee. He was playing a small stringed instrument, a dotara, and dominating the group as much by the sheer manic energy of his performance as by his singing: “Never plunge into the river of lust,” he sang with his rich, velvety voice, “for you will not reach the shore./ It is a river without banks,/ Where typhoons rage,/ And the current is strong.”

The three men are old friends and their voices are perfectly complementary: Paban’s resonant and smoky, alternately urgent and sensuous; Debdas’s a fine tenor; while Kanai’s was softer, more vulnerable, tender and high pitched – at times almost a falsetto – with a fine, reed-like clarity. As Paban sang, he thundered away at the dubki, a sort of small rustic tambourine. Kanai, by contrast, sang with his sightless blue eyes fixed ecstatically upwards.

A Baul singing on a train in West Bengal

Throughout their 500-year history, the Bauls of Bengal have refused to conform to the conventions of caste-conscious Bengali society. Subversive and seductive, wild and abandoned, they have preserved a series of esoteric spiritual teachings on sex, asceticism, philosophy and mystical devotion. They have also amassed a treasury of beautifully melancholic and often enigmatic teaching songs that help map their path to inner vision. Travelling from village to village, no man owning anything but a multicoloured patchwork robe, they sit in tea shops and under roadside banyan trees, in the compartments of trains and at village bus stops, busking their ballads about love and mysticism, divine madness and universal brotherhood to gatherings of ordinary Bengali farmers and villagers.

As Kanai explained, “When you first become a Baul you have to leave your family and for 12 years you must wander in strange countries where you have no relatives. There is a saying, ‘No Baul should live under the same tree for more than three days.’ At first you feel alone, disoriented. But people are always pleased to see the Bauls: when the villagers see our coloured robes they shout, ‘Look the madmen are coming! Now we can take the day off and have some fun!’ Wherever we go, the people stop what they are doing and come and listen to us. They bring fish from the fish ponds, and cook some rice and dal for us, and while they do that we sing and teach them. We try to give back some of the love we receive, to reconcile people and offer them peace and solace. We try to help them and to show them the path to discover inner knowledge.”

It was the article I then wrote that started me on the path to my new book, Nine Lives, which is about how south Asia’s diverse sacred traditions, like those of the Bauls, are managing to survive in the new India. Much, of course, has been written about how India is moving forward and transforming itself at the most incredible rate – the economy has been predicted to overtake that of the US by 2050 – but so far little has been said about the way these huge earthquakes have affected the great Indian traditions of mysticism, monasticism, music and dance.

Nine Lives explores this process through nine personal stories – a Sufi, a possession dancer, a Buddhist monk, a Jain nun, a tantric and so on, each story aiming to show how faith and ritual are clinging on in the face of India’s commercial boom. Each life represents a different religious path, and is intended to act as a keyhole into the way that each vocation has been affected in the vortex of rapid change, while revealing the perhaps surprising persistence of faith and ritual. The idea is to find out what it means to be a holy man, a mystical musician or a tantric minstrel seeking salvation on the roads of modern India as the Tata trucks thunder past.

William Dalrymple rides pillion behind a naked sadhu

My travels for the book have led me to meet some extraordinary individuals. In Kannur in northern Kerala, I met Hari Das, a well builder and part-time prison warden for 10 months of the year, who polices the violent running war between the convicts and gangsters of the two rival political groups, the far-right RSS and the hard-left Communist Party of India. But between January and March, Hari has a rather different job. Though he comes from an untouchable dalit background, he is, nevertheless, transformed into an omnipotent deity for two months a year, and as such is worshipped as a god. Then, at the end of March, he goes back to his prison job.

On another trip, travelling in the deserts of Sindh in Pakistan, I came across the Shah Jo Raag fakirs, custodians of one of the greatest and most unusual Sufi traditions in south Asia. Every day they sing the verses of the greatest poet in the Sindhi language, the 18th-century Sufi master Shah Abdul Latif of Bhit Shah. Latif is the province’s most revered saint. He died in 1752 and, since then, his music and poetry have been performed by his hereditary fakirs every night in front of his tomb at the shrine where he once lived.

My eureka moment, when I had the idea of bringing all these different traditions together, and putting them on stage, came during this January’s Jaipur Literature Festival. At the festival, we have always had a strict rule that the writers must shut up at 6.30pm and hand over to musicians and dancers. In some cases, however, we have found that mixing music, poetry and readings can actually work very well.

One of the most remarkable events this year was an evening mixing Baul poetry with Tamil hymns sung by Susheela Raman, a celebrated London-born Tamil vocalist. The “thevaram” songs that Raman sings are taken from the seven volumes of devotional hymns written by the south Indian saints, first performed more than a thousand years ago in Tanjore and the other great temples of Tamil Nadu. By the end of the festival, as the different elements fell surprisingly effortlessly into place, the idea of the roadshow was born.

So, next weekend we open the tour in front of 3,500 people at the Barbican, before heading to Bristol and Ireland, then on to India and Pakistan. In the spring we have dates in Australia, France and the Netherlands and, if we can raise the sponsorship, will take the tour to the US in May. Finding people eccentric enough to fund all this has been almost as much work as getting the Bauls, the fakirs, and the dancers to have their photographs taken, apply for passports and visas, and getting police clearance. Much remains to be finalised. Even more could still go badly wrong. But, if that’s the case, then maybe there will be a road movie or even another book out of it, though next time the idea of launching it with a small drinks party in Holland Park could seem awfully tempting.

‘Nine Lives: In Search of the Sacred in Modern India’ (Bloomsbury, £20) is published on October 5 and is available from the FT Bookshop at £16 plus p&p, tel: 0870 429 5884 or go to www.ft.com/bookshop.

An evening of music and readings curated by William Dalrymple is at the Barbican (www.barbcian.org.uk) on September 25