On an Air France flight from Paris to Havana, Dag Halvor Nylander has fallen silent. Over the previous hour, the Norwegian diplomat has had answers for everything. Now, as a flight attendant serves him coffee, he pauses and reconsiders a question.

Three days later, at a secluded compound beside a beautiful lake in the heat and humidity of Havana, Ivan Marquez is taking a similarly long time to come up with a response to the same query. The leading peace negotiator for the Revolutionary Armed Forces of Colombia (Farc) smiles as it is translated from English to Spanish, puts his head to one side and opens his mouth – but no words come out.

At his office in the Colombian presidential palace 24 hours later, Sergio Jaramillo Caro is also struggling to find the right words. Thumb and forefinger pressed together on his bottom lip, the Colombian president’s peace adviser takes an uncomfortably long time to speak.

The question is very simple: do they trust each other? The answer is the difference between war and peace. These three men – the shaven-headed Norwegian diplomat, the Marxist guerrilla and the Oxford and Cambridge-educated presidential adviser – are the most important players in one of the world’s most important peace processes. At stake is the end of the longest-running conflict in the Western hemisphere.

This story can begin in many places: in 1966, when the Farc first took up arms against what it saw as repressive policies towards the rural population; in 2002, when the last peace process fell apart and a rejuvenated Farc returned to the battlefield; in 2006, when a hardline president, Álvaro Uribe, ordered a renewed crackdown and gave his defence minister, Juan Manuel Santos, carte blanche to do what he felt was necessary; or in 2010, when Santos became president and decided that time was ripe for peace. Let us begin there, three years ago – although we may have to dip back further from time to time.

To call Santos a protégé of Uribe would be too much but it is fair to say that the new president wouldn’t be in power if it wasn’t for the support of the old one. Uribe’s presidency was controversial, marred by a stream of corruption allegations and human-rights abuses by the armed forces – armed forces under the supposed control of Santos.

Santos’s deputy at the ministry of defence was Jaramillo. The two men launched an aggressive campaign against the Farc, killing commanders and demobilising hundreds of guerrillas. But once Santos graduated to the presidential palace, with Jaramillo joining him as national security adviser, the two men agreed that the military campaign had taken them as far as it could. Two of the most hawkish politicians in Colombia decided it was time to make peace.

“This has dragged on for a long time at a cost in human lives,” says Jaramillo, sat in a small room some 50 paces down the corridor from the president’s office. “The Farc is getting on in life. It’s a cliché but it’s a true window of opportunity.”

Jaramillo made contact with Farc leaders “through classic back channels” and within a few weeks secret negotiations to discuss a framework for proper peace talks had begun in Havana. There was, of course, that issue of trust. For talks to begin, both sides needed a moderator they were comfortable with. Think of a peace process, any peace process anywhere in the world, and the chances are that Norway will be involved in some way. Not that many people will know. There are at least 20 projects that the 12-member peace and reconciliation unit in Oslo is currently working on (those that are known include talks with the Taliban in Afghanistan, post-war mediation in Sri Lanka and, of course, the Farc talks in Colombia) but most remain secret, sometimes even to other members of the team.

It is the sort of painstaking, patience-shattering, never-getting-any-credit work that really should be carried out by the UN. But instead it is Norway, population five million, that has become the world’s peacemaker. The reasons why are fairly straightforward: they want to make the world a better place, they’re rather good at it and it gives them influence. “It’s a value-based, moral-based issue for us,” says Gry Larsen, Norway’s deputy foreign minister, who is responsible for the peace and reconciliation unit. “War and conflict causes so much suffering in the world.”

Their approach is different from many other Western nations. “We have told our diplomats, ‘You can talk to everybody. Talk to groups that few talk to.’ That has been the failure for the past 10 years in world politics. We need to go back to see if it’s possible to find political solutions.”

Sacrifices have to be made for peace processes to begin. Talking to the Farc and flying its members to Oslo means refusing to sign up to the EU’s list of terrorist groups. Getting Cuba on board means having a proper diplomatic relationship with them and not refusing to engage because of their human-rights record.

Nylander first came to Bogotá in 2006 as a young diplomat with fluent Spanish and an interest in Latin America. At the time the Colombian government, under Uribe, was engaged in peace talks with a far smaller rebel group, the eln, and Norway was involved as a mediator. Those talks collapsed but Nylander sensed that the mood towards the decades-long war was changing. Talks with the Farc were on the cards, he felt.

“I’d been telling them [his bosses] this ball would start rolling at some point,” says Nylander. “We had to be ready to contribute.” The foreign ministry’s relatively unbureaucratic approach to diplomacy helped. “There is strong support from the top and a short distance between diplomats and the ministers. There is also flexibility – we can respond very quickly.”

When Santos was elected in 2010 and Jaramillo started that ball rolling, Nylander was ready. He was involved in the secret talks – “They were intense, difficult, emotional” – and when the moment came to bring them out into the open, he was able to offer Oslo as the venue for the official launch. Over three days – and lots of Norwegian salmon – the two sides, and in particular Marquez and Jaramillo, got to know each other. “It was fascinatingly interesting to see how they got on,” says Nylander. “It was not a warm relationship.”

It was a start, though. After separate press conferences, the first stage came to a close and the negotiations moved to Havana. Cuba is, for all the obvious reasons, a good place to hold sensitive talks away from the constant glare of scrutiny. If the negotiations are to be successful there can be no hangers-on, no strategic leaks to friendly journalists, no distractions. In Havana, all sides can quietly get on with the job.

Cuba, like Norway, has a seat around the negotiating table. Its government is sympathetic towards the Farc, something that helped to persuade them to agree to talks. (The influence of Hugo Chávez was important, too. Following Chávez’s death his successor, Nicolás Maduro, has pledged that Venezuela’s backing will remain.)

Nylander is speaking from the back of a grey suv, part of a three-car convoy driving through the art deco centre of old Havana. A five-person team of Norwegian diplomats, including minister Larsen, has come to Cuba to check on the progress of the talks before heading to Bogotá to meet politicians, victims and charities. After meetings with Cuban ministers, the delegation is off to face the Farc.

The convoy slips off the main road a mile or so outside Havana. A smooth driveway leads downhill, winding its way through a thicket of trees. An officer in plain olive-green fatigues and Fidel-style hat takes a cursory look at the papers and waves us through. Beyond the checkpoint lies a beautiful lake surrounded by manicured lawns and palm trees. A series of villas dot the lakeside. It is where visiting heads of state and ministers stay during summits. But for the past six months, these villas have been home to the negotiators.

The Colombian government team has one cluster of houses and the Farc has another, while Nylander lives in the house in the middle. The largest and most imposing, a grey stone house perched on the top of a hill, is the temporary home of Ivan Marquez.

An avuncular figure with a closely cropped beard, round glasses and smiling eyes, Marquez is the Farc’s head negotiator. He is also a Farc commander of 20 years standing who has a $5m bounty on his head from the US state department, which accuses him of “directing and controlling… the murder of hundreds of people who violated or interfered with the Farc’s cocaine policies”.

When Marquez first sat down opposite Jaramillo he pointed out that the presidential peace envoy was also the national security adviser. “You are war and peace,” Marquez said. “Just like me.”

Marquez – again, like Jaramillio – now says he wants to be a man of peace alone. “We consider that wars are not eternal, that all conflicts have an end, and we think that this is also a very good moment to attempt reconciliation within the Colombian family.”

Marquez and his colleagues have tried to make their slightly impersonal villa feel more like home. Looming over the living room is a large banner featuring the face of former leader Alfonso Cano, staring out through his owl glasses. Another Farc icon is present, too: a cardboard cut-out of Simón Trinidad (currently serving a 60-year sentence in the US), standing and smiling with his arms crossed, is propped up against the French windows in one corner. Simón Bolívar is also here in poster form, looking stern.

The talks have a strict timetable. The two groups meet for 11 days straight then take a break for five days, allowing all sides to return home and confer. Then they come back and start again. The formal talks begin each day at 09.30 and end at 13.30. The negotiators gather in a room with a large rectangular table at the centre, up to 10 government officials on one side and up to 10 from Farc on the other. The two Norwegians and two Cubans sit at the end. No one chairs the discussion, nor does anyone take formal notes. Once everyone has taken their seats, someone starts talking. “Well,” says Jaramillo, “we’re grown-ups.”

Grown-ups, of course, take things seriously. There is, as Jaramillo admits, “no camaraderie”. The Farc sometimes spends afternoons playing football but hasn’t, so far, invited the government negotiators to join them. (Marquez laughs gently at the suggestion.)

The last time talks were attempted (from 1999 to 2002) they were much more informal. The two sides drank and smoked cigars together, everyone was invited – diplomats would dip in and out. Nothing got done and they fell apart. This time around it is far more formal, far less social – and much more productive. There are five parts to the agenda – from drug trafficking to the rights of victims – and already an agreement has been reached on the first section: land. The announcement of a deal was met with surprise in Colombia. Public support for the talks is strong but in an inverse proportion to hope for their success.

The biggest challenge will be justice. Crimes have been committed on both sides; tens of thousands of people have been killed. At one meeting in Bogotá, Larsen and Nylander meet the head of a charity that defends the rights of citizens caught in the middle of the war. Maria Antonia Amaya quietly lists the ways in which people have been affected: “Assassinations, illegal detention, murders, kidnapping, bodies disappeared, sexual violence, children abducted and children murdered.” The room falls silent.

For any deal to be accepted by the Colombian people, particularly by the victims, there needs to be some form of justice. “What it looks like is difficult to say,” admits Nylander. The balance between peace and justice is notoriously hard to get right. While many activists may have been happy to see Sudanese president Omar al-Bashir charged with genocide for crimes in Darfur, he remains president and the conflict in Darfur is not over. “People are looking to Colombia. When they design a transitional justice mechanism it will be a very important moment.”

Nylander says “when” not “if” and this general sense of cautious optimism is shared by almost everyone he and Larsen meet during the week. President Santos has given the negotiators a deadline of November. Elections take place in Colombia next year, something that gives a sense of urgency to the talks. Both sides believe that the best chance of a peace deal is with Santos and that elections – the ferocity of the campaign let alone the actual result – could scupper that. While the Farc realises that it can push Santos farther than he would like, it also realises that if everything falls apart and Santos loses, a new government will probably go back to war. And it doesn’t want that.

“As in all negotiations, each side wants to push the other as far as possible without pushing them over the cliff,” says Nylander. “But no one knows where the cliff is.” If a deal is struck – and there is enough confidence around the table to suggest it might be – the question is whether either side will be willing and able to fully implement it. The track record for both parties is not particularly impressive.

On the final day, with the delegation tired and beginning to think about the imminent flight home to Europe, there is an emotional reminder – if one were needed – of what is at stake. Soacha is a town of 400,000 who live in basic slap-dash brick houses flung onto the side of a mountain overlooking Bogotá. The roads are nothing more than dusty tracks, there is an army of stray dogs and the dozen police officers accompanying the delegation give the impression that this is a part of Colombia they would rather not be in.

Soacha is a microcosm of the consequences of the conflict. Around 40,000 of the town’s residents are here only because they were forced to flee their homes; this was also the site of one of the most gruesome episodes of the war. Military commanders gave incentives to units based on the number of guerrillas they captured or killed. In a scandal that became known as the “false positives”, young unemployed men in towns such as Soacha were lured away with the promise of jobs. They were then murdered and dressed up in guerrilla uniforms, allowing those units to inflate their numbers.

In a close and crowded small room on the first floor of a local ngo, three mothers sit down with Larsen to tell the story of their sons. Some are holding pictures. The stories are told haltingly, through an interpreter. Soon the mothers are crying, the minister is crying and the interpreter is crying. “You can find a hundred reasons why these talks will fail,” says Larsen. “We have to remember the victims and make it work.”

It will come down to trust. Do the Colombian people trust the Farc to lay down its weapons? Does the Farc trust the military to stick to a deal? And, at the heart of the issue, can two men, Ivan Marquez and Sergio Jaramillo Caro, trust each other? On the plane, Nylander’s answer is diplomatic; in Havana, Marquez will say only that “the ice has been broken” and the relationship is now “very respectful”.

In the presidential palace it’s 20.30 and nearing the end of a long day, although Jaramillo still has meetings to attend. In the gathering dusk, the peace advisor takes so long to answer the question that the silence becomes deafening. Finally, he speaks. “It teaches you to rethink the whole idea of trust. This is not about trusting people. It’s about behaving in a serious way over a period of time.”

This, he says, begins to build trust, even if it’s not there yet – indeed, it may never be there. Only once a deal has been agreed, signed and implemented can any of the men around the table be sure that they trust each other. “Trust is not the beginning,” says Jaramillo. “It’s the end.”