If there are clues to explain what happened, they lie behind the open door of the third hut on the left at the entrance to the poor, remote village of Subalpur.

It was here that a 20-year-old single woman was found in the company of a married man from another village on Monday afternoon. Dragged out by her neighbours and tied to a tree while the village council deliberated, she was then raped by up to 15 men as punishment for the illicit liaison.

The mud-walled home, a single room under a rusted tin roof, is empty now. The woman is in hospital and under police protection. Her family are in hiding. Her alleged lover, an older mason, has run away. No one in his village, six miles away across the dry wheat and oil seed fields that spread a parched patchwork across this corner of north-east India, has seen him for days.

On the wall of the home the woman shared with her mother are posters of stars of local Bengali-language films, a shelf supporting a small shrine, a mirror above a pot of moisturising cream and a rack of a dozen gold and red bangles.

All the neighbouring houses have a shrine; none has bangles or branded toiletries.

Some villagers in Subalpur angrily denounced the woman, named simply as W in accordance with strict anonymity laws protecting rape victims, as a "woman of bad character" who "spoiled the atmosphere of the village" by going against local customs. Some alleged she had worked as a prostitute – a charge denied by her family.

But interviews with relatives, officials and neighbours reveal a different story: of a young woman who was unable to accept the stifling claustrophobia and crushing poverty of a rural hamlet in a country where, despite massive economic growth over recent decades, opportunities for the most marginalised remain rare.

Reverberations of the incident have swept across India, which is struggling to deal with a wave of sexual violence. A 51-year-old tourist was gang-raped in Delhi earlier this month, the latest in a string of attacks on foreigners.

The gang-rape and murder of a 23-year-old Indian woman in Delhi in December 2012 prompted grief and outrage across the country, with thousands taking to the streets demanding tougher laws, better policing and a shift in cultural attitudes. But any reforms have had little effect in villages like Subalpur.

Soham, the woman's 23-year-old brother, remembered how W had grown up rebellious.

"From her earliest childhood, she did not give heed to the elders. She followed her own whims," he said.

But like her peers, W also missed most of her education in the rudimentary government school two miles from Subalpur to play and work in the fields with the other children. No adults in the village can read or write; few of the teenagers can either.

Four years ago, against her parent's will, W contacted a local agent who arranged a job in Delhi, more than 1,000 miles away. Though the capital acts as a magnet for young people from poor, rural backgrounds from all over India, none from Subalpur had ever gone further than the local town, Suri, 22 miles away. Many of the women had never even been there.

"I've never been to a town. Our men are labourers in the fields. We are with the children. Why would any of us go to a town except to do something that was no good?" said Manika Tudu, 22, a neighbour.

W got a job as a cook on a salary of £40 per month, a fortune in a village where labourers earn nothing for much of the year. A government scheme guaranteeing 100 days of labour each year provides a week or so of employment at best. In Subalpur, though none starve, few eat their fill.

"We don't go without for days on end but it never feels like there is enough," said Padmuni Tudu, 37, who could not remember when she last ate meat. Though all the villagers qualify for government rations of nearly free basic foodstuffs and fuel, they only ever receive the latter.

Five months ago, homesick for the village despite the hardship, W returned from Delhi. She had some trouble adapting. In Subalpur, people defecate in the fields. She had got used to a toilet.

But the biggest problem was social. "She was shunned," her brother said.

Living alone with her mother – her father died some years ago – left W vulnerable too. Her liaison with the mason was soon common knowledge, and far from popular. Any relationship with another community is forbidden, local officials said, and involvement with a Muslim, as in this case, particularly shocking.

"We found them together. The women took her and the men took the boy and we tied them to a tree while the village council took their decision," said Manika Tudu, the neighbour.

The people of Subalpur are from India's tribal communities, sometimes called Adivasi and among the most marginalised and exploited people in the country. Around 8% of the total population, their communities are run by unelected councils, which settle disputes. Similar institutions dispense rough justice across much of India's countryside, where people shun a police force and judiciary seen as corrupt, slow and distant.

"This is our way. We don't go to the police. If there is a problem, we settle it among ourselves," said Fulmoni Tudu, 40, whose husband is among the 13 men currently detained for the alleged gang-rape. Even W's brother backed the system, though he said a "beating" would have been a fair punishment.

All witnesses agree that the council, led by the headman, decided to impose a fine of 27,000 rupees (£280) on W and her alleged lover. The man's relatives sold their jewellery and paid. But the enormous sum was well beyond the means of W's family.

There are different versions of what happened next. In the detailed account given to the police by W and her mother, recounted to the Guardian, the woman describes how the headman told the men that, as she could not pay the fine, they were free to "enjoy her". She was then led to a rough bamboo and palm leaf hut only yards from the headman's house and repeatedly raped. Subsequently, she has said, villagers confined her to her home and threatened her with further violence if she informed authorities. However, nearly 48 hours later, her mother and two brothers managed to smuggle her to a local clinic. When she was then transferred to the district hospital suffering severe blood loss, police were alerted.

Villagers say this account is all lies.

"How could our husbands do this? We were with them all through the night. And if she has been raped by so many men how can she talk? She has made up this story to escape paying the fine and to cover up her bad behaviour," said Manika Tudu.

But senior police officials say evidence so far gathered indicates W's story is genuine. Medical examinations show she was raped by between "five and fifteen", one said. Thirteen men have now been detained.

West Bengal is a particular blackspot for sexual violence. In October a woman died of burn injuries after being raped twice by the same group of men, once as she returned from a police station where she had recorded a statement about the first attack.

The state is governed by the Trinamool Congress party (TMC), led by Mamata Banerjee, a firebrand political outsider and one of the most powerful women in India. Political rivals have quickly seized on the opportunity to score points.

Robi ul Islam, a local official of the Congress Party, said the TMC ruled through "hoodlums" and so were responsible for rising violence while Sathi Pal, a women's officer with a local communist faction, blamed Banerjee's "capitalist ideology".

Groups representing India's tribal people said they were afraid the incident would be exploited by "powerful people". Tens of millions of tribal people have been forced off the land in recent decades on flimsy pretexts.

"The description of 'kangaroo courts' will legitimise further attacks on our culture and more attempts to force us into further poverty," said Sunil Soren, a local tribal rights activist.

For the victim's family, there are more immediate problems. The fine imposed by the village council still has to be paid. They will now have to borrow the vast sum outstanding and face decades of crushing debt if they want to avoid expulsion from the village.

"We have no choice. We have nowhere else to go," Soham, the brother, said.