A remote valley east of the Peruvian highlands is the perfect place for growing coca.
Peru now produces more cocaine than any other country, and this is where more than half of it originates. But there is no easy way to smuggle it out, so traffickers hire young men to carry it on foot.
They are the mochileros - the backpackers.
At any moment there are likely to be hundreds trudging over mountains and through the rainforest with pure cocaine worth thousands of dollars on their backs.
It's one of the most perilous jobs in the cocaine industry.
A teenager rips an over-sized tropical leaf from a branch. He strips the stalk, then using both hands, he wrings it out.
The moisture runs as though from a tiny tap - pure and sustaining.
On a journey that will take him through dense jungle terrain, knowing which plants can quench thirst is one small survival technique.
Daniel is a mochilero - one of thousands of young Peruvians who hike an illicit cargo of cocaine from the valley of three rivers - the Apurimac, Ene and Mantaro - to secret stash points or clandestine airstrips from where it will be moved on by other means.
Known locally as the Vraem - a contraction of the Spanish Valle de los Rios Apurimac, Ene y Mantaro - the huge valley is one of the poorest regions in Peru.
Daniel lives here in a village with his parents and siblings - and at the age of 18, he is a veteran of the cocaine business.
“I started working with drugs when I was 14,” he says. “I got to know the local boss, and I was hired to work in a laboratory producing cocaine from the coca leaf - I've known how to use the chemicals since I was 15. At 17, I began transporting the drug.”
Most of the journeys Daniel undertakes are lengthy - two weeks to reach the destination and 10 days to return home. He carries 15kg of cocaine. It is precious cargo, and his job is dangerous - far too dangerous for him to be identified publicly.
In Peru, a kilogram sells for around $1,200. Wholesale in Miami its value is 20 times greater. Sold to drug users in London or Paris, this innocuous looking white powder is worth upwards of £50,000 ($75,000) a kilogram.
Many mochileros move in small groups of 10 to 20. But Daniel treks with 100 to 150 others, and together they move drugs in industrial quantities.
These journeys take him north out of the valley. Or he travels in a south-easterly direction, passing close to the tourist mecca of Machu Picchu, and towards the city of Cuzco.
The mochileros are well organised and prepared for attacks - either from rival groups or the police.
“The guys at the front have big guns, like a long-barrelled Galil or a Mauser. Those at the end of the line carry pistols, like a Browning. Our lines are very long, and we walk with two or three metres between us. If there's an attack, it's the guys up front who fall first. When you're at the back and hear the shooting, you just run and escape.”
He says they buy ammunition from corrupt police officers. Often it is hidden in the buckets of food scraps and rubbish dumped outside the police barracks, from where the mochileros retrieve it.
But assaults and shoot-outs are not the only hazards. The journeys themselves are physically demanding, taking these young men high into the Andes on ancient Inca trails, and down into the Amazon Basin along tracks hacked through virgin forest. It can be treacherous.
“On one of the routes, you pass a mountain, and the drop to the river below is maybe 800m. You go along a path that's so narrow you have to walk sideways with your back against the mountain, carrying your backpack in front. Sometimes it's slippery, and people just fall.”
Daniel does not smile much. His face is quite immobile, even when he is talking. He is small and muscular, like a battle-hardened soldier, and he is old beyond his years. On every journey Daniel has undertaken, three or four mochileros have lost their lives.
“I've introduced family and friends to this business. We travelled together. But 10 of them have died. Some were close relatives, cousins with the same surname as me. It's very painful to leave your cousin behind on the trail somewhere.”
Of those 10 young men, four fell into the river, the others fell victim to minor injuries that meant they were unable to continue. With treatment they would have survived - but left alone, with limited food and water, they died.
“Maybe you get bitten by an insect, and get an infection. There are plants that can heal you, but they aren't available everywhere. Or you fall or get cut. Your feet swell, and they change colour. Then you can't walk. Your foot rots and ants enter the wound. You can't go on because of the pain. And there's no-one to help you - the others just leave you. That's how your life ends,” he says.
“You try to help them on the first day, but then you get tired and they have to stay behind.”
In this line of work, nobody's responsible for [you], or cares, when you die.”
The fear of losing his own life has not yet persuaded Daniel to stop. The money is too tempting. He is paid $2,000 for every round trip - more if he takes his own weapon. It is a small fortune in the valley.
“If you think about the risks, then there are risks. If you think you could die, then you could die. But if you say no to those thoughts, faith moves mountains.”
The coca bush is an unassuming plant - its leaves are not luxurious, and it does not grow tall.
In the Vraem, it is everywhere.
Massive plantations stretch as far as the eye can see. Young people like Daniel have grown up in this coca culture - it is part of life.
In every village, freshly picked leaves are regularly tipped from sacks on to large plastic sheets. They are kicked out with bare feet, spread evenly to dry in the sunlight.
Most farmers in the Vraem grow some coca - and that is not illegal. Shops sell leaves by the bagful, and when chewed or made into tea they are a mild stimulant and appetite suppressant, and can also help with altitude sickness.
Coca leaves may also be used to try to divine the future. For many Peruvians the plant is revered and sacred. It connects them to their Inca ancestors and even those who came before.
But although it is not against the law to grow coca, it is illegal to process the leaves into coca base from which powdered cocaine hydrochloride is made.
Supplying the leaves to narco-traffickers is also, of course, prohibited.
At the heart of the valley is the town of Llochegua, a commercial centre that serves tiny, far-flung communities.
The only visible signs of disposable income are the expensive 4x4 pick-up trucks - the go-to vehicles of narcos across Latin America.
The mayor, Juan Carlos Bendezu Quispe, says 90% of the farmers in his district grow coca.
“It's a big problem, but it's the only crop that sustains people. Coca's harvested four times a year. Coffee's only harvested once, and its price is rock-bottom,” he says.
I'm sure if you lived here, you would grow coca to feed your family too.”
“In Llochegua, for every 100 students who finish high school, maybe 10 go to university, although only two or three will finish. And the other 90? They end up growing coca.”
Many become mochileros too. At least a third of the cocaine produced in the Vraem is transported on their backs.
While Daniel carries it long distances, far away from the valley, others take it to airstrips closer at hand, hidden deep in the jungle.
One law enforcement source described how during a two-week period in October seven moving columns were being monitored, each of around 100 backpackers, “lined up like wagon trains”.
The flights come in with thousands of dollars of cash on board, and take off loaded with more than 300kg of coca base or cocaine.
In the past year-and-a-half, more than 250 illicit runways have been blown up by Peru's specialised drug police and the military.
But repairing the blasted airstrips takes only a few days, and new ones continue appearing in ever more remote locations. During the day planes buzz overhead on their way to Bolivia - the main distribution point for cocaine from the Vraem.
Drugs also move by road. But there are military and police checkpoints, and landfalls may block highways in the rainy season.
A fit, committed mochilero - which is what Daniel is - may well be a better bet to ensure delivery of one of the world's most expensive consumable products.
Comandante Luis Enrique Diaz peeps out from under a peaked, camouflage cap, surveying a coca plantation that tumbles down the valley towards the river below.
Commandante Diaz of Peru's anti-narcotics police is serious, sturdy - and he is Daniel's adversary.
“We need intelligence to know where the mochileros will pass, and to be able to cut off their routes,” he says.
“Often it's far away and very inaccessible. Then we hide and wait to ambush them. Sometimes we stay there for four or five days. That's the only way to do it.”
These people are armed, and prepared to defend the drugs. So both police officers and mochileros die in these encounters.”
Most people in the valley know of somebody who disappeared without explanation, or whose dead body has turned up in a remote location.
That is what happened to Alain Leon, a 23-year-old living far away from his family in Ayacucho, a city high in the Andes.
But Alain was not killed in a shoot-out, he was stabbed.
His family was told simply that people in a distant village had found a body bearing knife wounds.
“When we called the police station they said we had to come in the next two days to collect him, otherwise he would be buried in a common grave,” says Alain's brother, Richard.
But the family was too poor to retrieve his body from the highland town where it had been taken, and they have never managed to find out exactly where he was buried.
The absence of a proper funeral intensified the trauma especially for Alain's mother, Eduarda Ramirez de Leon, who half-believes her son is still alive somewhere.
It is the stuff of nightmares.
Alain had told his family he was working as a driver carrying goods by road between highland towns.
Alain used to say he wanted money no matter what, and he was determined to get his own car.”
“He was a very ambitious young man,” says Richard.
They had no idea he could be mixed up with drugs, but the village where he was found is on one of the routes used by mochileros.
Probably he was working as a mochilero and died in a skirmish with a rival group or criminal gang intent on stealing his cargo.
There are other perils too that may bring an early end to a mochilero's career.
The town of Andahuaylas has a nickname - “White City” - you can probably guess why.
Around town there are new, modern homes, many of them vacant and pasted with notices declaring they have been seized by the authorities. Property is one way of laundering drug money in Peru.
The prison sits on the edge of town. In spite of its control towers and barbed wire, the carefully painted blue and yellow walls give it a jaunty appearance in the afternoon sunlight.
Inside, a large mural of Christ is painted on one wall. Of the 332 inmates here, more than half are serving time for drug offences, and of those, the majority are backpackers.
Thirty-seven of them are women. Ranging from teenagers to middle-aged mothers, and even grandmothers, they have been convicted of transporting cocaine on foot and by road.
Roxana has the fresh, open face of an innocent.
She is 26 years old, quietly spoken, and is serving a sentence of 12 years with no remission for trafficking coca base. She was picked up with bricks of the drug strapped to her body under her clothes.
“I was at a private university studying accountancy, and I needed money for college materials. My parents couldn't help me because they are poor, and in any case I wanted to be independent,” she says.
A woman Roxana knew offered her a job carrying coca from Andahuaylas to Cuzco. There were three of them. First they had to trek a few hours out of Andahuaylas into the mountains in the middle of the night to get to the pick-up point.
Once they had the cargo, they would travel by road in different vehicles. The journey there and back took a week, and for Roxana it was the first of several.
When she was stopped in a taxi by the police five years ago, she was carrying 12kg of coca base, worth thousands of dollars. But she was paid just $100 for these trips.
I just needed money to pay my bills. But I was used by that organisation, I can see that now.”
Roxana is full of regret. “There is nothing more beautiful than liberty,” she says.
In the male facility next door, 139 inmates have been convicted of drug crimes, the vast majority of them mochileros.
An anti-drugs organisation, Cedro, funded through the US Embassy in Lima, carried out a study two years ago of imprisoned young, male mochileros and found that most had not finished secondary school, and were unaware of the penalties they faced.
“Most knew they were committing a crime,” says the report's author, Laura Barrenechea.
“But they didn't understand that crime was aggravated if they travelled in a group of more than three, or if any of them carried a weapon. So they could end up with a sentence of as much as 15 years.”
She points out that although the jails are full of mochileros, none of the drug kingpins have been caught.
In the Vraem the cocaine business is controlled at community level by clans and families. Locals have an idea about who they are, but the important drug-traffickers always seem to escape imprisonment.
“And there's an important detail,” says Laura Barrenechea.
“Most of the mochileros told us when they were caught by the police it was because of a tip-off.”
Often they had declared their intention of leaving the business, of making that their last trip. That made them vulnerable. And the suspicion is that it was their bosses who turned them over to the police.”
So if mochileros want to retire, they risk becoming dispensable.
They may also be targeted in police operations if their boss betrays them to distract attention from a larger consignment travelling by a different route.
“That's what a lot of them believed,” says Barrenchea. “That their small group was sacrificed so a more important load of cocaine could move freely out of the Vraem.”
On a hillside high above the town of Pichari, the soil is the colour of ginger biscuits.
Francisco Barrantes and his wife, Victoria Canchari, are inspecting their coca crop. He rubs the leaves between thumb and forefinger, and a cloud of butterflies emerges from one bush.
This is a bad sign - the leaves are being destroyed.
It means Enaco, Peru's state coca agency, which buys leaves to make legal coca products, will not want them. The only buyers for spoilt leaves are the narcos.
But Francisco Barrantes does not only sell the coca chewed by caterpillars to drug-traffickers, he sells them most of his crop.
“According to the law, coca-farmers should sell their coca to Enaco. But the agency pays a lot less than the narcos. And the drug-traffickers come to the field and buy it here, so it's much easier for us,” he says.
“It doesn't make sense to sell our coca to Enaco at a lower price.”
As secretary general of the Federation of Coca Producers in the valley, he is well aware of the bigger picture. He knows families whose boys have died working the backpacker routes.
Sadly I'm an unwilling partner in this business. I know the coca I sell ends up in the backpacks of young mochileros in this area. I'm also aware of the impact of all of this in other countries.”
So Barrantes is planning on joining a government-sponsored crop substitution programme. The government will send in agro-engineers to advise on the swapping of coca for coffee and cocoa.
Ironically, those are the crops he used to grow here 30 years ago.
He abandoned them for coca, which needs far less tending, when the Vraem became a war zone in the 1980s.
For years, Sendero Luminoso (Shining Path), a Maoist guerrilla organisation, fought Peru's armed forces.
Together, they brought bloody mayhem to the valley and its people.
A small number of Sendero Luminoso guerrillas still operate in the Vraem. They too are involved in drug-trafficking, and they control some of the backpackers' routes.
Their presence explains why there has been no forced coca eradication in the valley as there has been elsewhere in Peru.
Last year, more than 300 sq km of coca were destroyed in other coca-growing regions further north.
Peru was lauded by the United States, even though the programme does not seem to have visibly dented cocaine production.
It is not surprising, given the economic supremacy of coca in the valley, that the farmers are resistant to eradication.
Francisco Barrantes says there could be social unrest if it is enforced. During the war, he was one of hundreds of campesinos who joined local militia to fight Sendero Luminoso.
Now alliances have shifted - Sendero has declared it will support the coca farmers if government agents arrive to pull up coca bushes.
So it is a stalemate. Coca production continues in the valley, and Daniel, the mochilero, is still in business.
But perhaps not for much longer.
“When I've saved enough I'll stop,” he says.
The money Daniel makes from the drug business feeds his family, but like many other backpackers he knows, his main motive for doing this work is to pay for his education.
My family are supporting me. They say I should continue in the business for now, and next year I can devote myself to studying.”
So far Daniel has accumulated $15,000, bought a piece of land and a small house. He has eschewed the life of a teenager and remained utterly focused.
“I don't have time to hang out in the streets. I used to have a girlfriend, but not now. When you have this job, your girlfriend isn't happy. And if you don't take her out, who will she go out with? She might end up betraying you. So it's better just to be alone and concentrate on the job.”
Daniel's ambition is to study law at university in Ayacucho. Then he wants to return home and become mayor.
“In five years, I will have finished university and be working to change first my village, then the valley, then my region and the rest of Peru. I won't be involved in the drug business, I'll be thinking about how to change my country,” he says boldly.
And he has a radical vision not only for the valley, but also for Peru.
What I have at heart is a dream to change all this, so we're not just producing drugs. In five years, we could legalise coca, and look for new markets producing and exporting medicines to other countries.”
That is Daniel's plan.
No doubt he has spent a lot of time thinking about it on those arduous, hikes across some of Peru's most difficult terrain.
But the cocaine trade has become part of Daniel's DNA. He has grown up with coca - picked it, dried it, processed it, packed it, carried it, risked his life for it, and made a lot of money.
Will he be able to leave this life? Will he be allowed to? There are powerful forces at work in the valley. There may be people who decide Daniel knows too much.
And what are the chances of him surviving as a mochilero until the year is over?
Daniel's name has been changed for his own safety.