For Daniel Guerra, an aspiring Brazilian sailor keen to travel the world, the job ad was a dream come true.

A British yacht owner was seeking two deck-hands to help sail his boat from Brazil across the Atlantic, one of the great ocean journeys.

There would be no salary, but all expenses paid - and, crucially, Mr Guerra would gain some of the sailing experience he needed to qualify as a sea captain.

"My dream was to become a captain and go work in Europe," remembers the 43-year-old, who saw the advert from an online sailing recruitment agency.

"So I was super happy, knowing that my path to my dream was beginning."

Things looked even better when Mr Guerra and his fellow recruit, Rodrigo Dantas, 32, met their new British employer.

They had feared he might be some snobbish yachtie or posing Instagrammer, who would make sure they knew who was boss.

But no. George Saul was a smiling, friendly figure, who did not insist on formalities. The sailors, he said, could even call him by his nickname - "Fox".

"I used to work on some boats and the owners were old, super demanding, super rude and talked down to me," adds Mr Dantas. "He was like, very cool, very friendly."

Fox even passed the approval test of Mr Dantas’s parents, who were worried about their son doing such a long journey on a yacht owned by a total stranger, and asked to meet him for themselves.

To borrow the old sailing expression, they liked the cut of his jib. They learned that Fox had brought the Rich Harvest over to Brazil for renovations, and wanted a competent crew to sail it back to Europe on his behalf.

As well as the rookies, Mr Dantas and Mr Guerra, there would be two others, including a qualified captain.

"I said: 'Look, watch out for my son'," remembers Mr Dantas’s father, João. "He said: 'Don't worry, I'll take care of Rodrigo.'”

As it turned out, his parents were not the only ones who wanted to check that all was well on board the Rich Harvest.

Before the departure from Brazil, local police spent around six hours searching the yacht for drugs, with the help of a sniffer dog.

They did not find what they were looking for, though, and the sailors assumed it was just a routine check.

They had heard stories about cocaine being planted on boats, and now at least knew they were in the clear.

"When you travel through an airport... your bags go through the X-ray machine," says Mr Dantas. "So I thought, well, it's an international trip and they're coming to inspect the boat."

Such worries were far from their mind when they eventually embarked on their epic journey on 4 August 2017, the Brazilian coastline slowly receding behind them.

With them were an additional crew member from Brazil and the yacht's newly hired French captain, a replacement for a previous British captain whose sailing skills had not proved up to scratch.

Fox, meanwhile, had made his way back to Europe by plane two days before.

"It was a beautiful day, perfect weather, sun," recalls Mr Guerra, who posted a message of thanks to Fox on his Facebook page.

It read: "I'm really grateful, Fox, for this... chance to learn and for our bond that has made me stronger. Thanks mate."

After two weeks of sailing, the yacht developed engine problems, forcing it to stop in Cape Verde, an archipelago off the coast of West Africa.

Once more, Mr Guerra and Mr Dantas found reasons to look on the bright side. The islands are a tourist paradise, and Fox said he would wire them money to enjoy themselves while repairs were done at a local marina.

And when yet more police came to search the vessel, Mr Guerra was not worried.

"They didn't find anything in Brazil," he thought to himself. "They won't find anything in Cape Verde either."

The Cape Verdean police were even more thorough than their Brazilian counterparts, using specialist cutting equipment to open up the yacht's innards.

Hidden inside below false floors, they found nearly 1.2 tonnes of cocaine - worth an estimated £100m ($134m) if sold on Europe’s streets.

"I felt that all my freedom was going down the drain,” said Mr Guerra. "I was furious, couldn't accept what was happening, you know? I’d been really fooled.”

In March 2018, the crew went on trial in Cape Verde, protesting their innocence.

They had never even heard of Rich Harvest or its owner until they answered the job advert, they insisted.

They were sentenced, however, to 10 years in jail each - in what was hailed as one of the country's biggest busts.

But while the haul was impressive, the man Brazilian police regarded as the big catch got away.

They believed that the mastermind of the operation was Fox, whose yacht was first drawn to their attention by a tip-off from the UK's National Crime Agency (NCA).

Brazilian police believe he was the leader of the operation to smuggle the drugs.

In August 2018, Fox was arrested in Italy, where Brazilian police filed extradition proceedings. They wanted him to be returned to Brazil to answer the allegations against him.

But the paperwork arrived too late, and he was freed - much to the frustration of Brazilian police inspector Andre Gonçalves.

He feared that Fox had subsequently gone into hiding.

"We were left with that feeling that after all our work, we’d never get to the bottom of it," he told the BBC. "It was very, very frustrating."

Mr Gonçalves said his team had kept both Fox and the yacht under surveillance in Brazil. They believe the "renovations" on the boat were partly to fit it with secret compartments, and that the drugs were loaded on to the vessel before the sailors were hired.

Mr Gonçalves admits that at first, he presumed the four sailors were involved too.

"If someone is on a boat that's full of drugs, you think that person must have something to do with it," he said.

But as he dug into their backgrounds, he could find nothing previously linking them to the drug world or to Fox.

"The deeper I went I still couldn't find a connection… but at the same time it strengthened the evidence we had against Fox."

The sailors' pleas of innocence also got backing from an unlikely source - fellow Briton Robert Delbos, a man who was alleged to be an accomplice of Fox.

Delbos, 71, is a convicted drug trafficker, having been jailed for 12 years in 1988 for attempting to smuggle 1.5 tonnes of cannabis into the UK.

Before the Rich Harvest left Brazil, Mr Gonçalves's team observed Delbos supervising the first stages of the yacht's renovations.

They initially suspected he was fitting secret compartments, and filed successful extradition proceedings for him around the same time as those against Fox.

Delbos spent months in a Brazilian supermax prison awaiting trial, but he too said the drugs were later planted without his knowledge.

He was acquitted after the judge in his case ruled it could not be proved that he knew about the smuggling plan.

In an interview with the BBC, he claimed that even drug traffickers had codes of ethics, and that Fox had violated them by using innocent sailors as mules rather than hiring professional smugglers.

"This is completely beyond the pale. I mean, you don't do this," he said.

"He was a stupid man who was greedy. Instead of paying the crew properly and getting himself a professional, bloody smuggling crew - he hired four innocent guys."

As doubts about the sailors' guilt grew, their families began a campaign on their behalf, which became a cause célèbre in Brazil.

In 2019 their convictions in Cape Verde were overturned, and they were allowed to go home.

Fox, meanwhile, has never faced trial, and returned to the UK.

The 41-year-old lives in Norwich in eastern England where he grew up, attended college locally, and was an accomplished amateur yachtsman - sailing off the nearby Norfolk coast.

Today, he resides in a Norwich suburb and runs a property firm.

He belonged to a local business networking association, and on his social media feed last March, posted photos of himself with the city's then Lord Mayor, James Wright.

There is no suggestion that Mr Wright was aware of the accusations against Fox.

The BBC tracked Fox down as he arrived at one of his networking association's weekly business breakfasts, at a Norwich hotel.

He declined to comment on the Rich Harvest and the sailors' ordeal.

Asked about the allegations that he was a drug trafficker, he replied: "I'm not."

An NCA spokesperson said if Brazilian police still wished to pursue the case, they would have to file an extradition request.

Brazil's ministry of justice said it did not comment on individual cases.

Meanwhile, Rodrigo Dantas and Daniel Guerra are trying to rebuild their lives in Brazil, their dreams of becoming yacht captains abandoned.

Mr Dantas says he struggled to find sailing work on his return home, with some employers assuming he must have been guilty after all.

Mr Guerra’s round-the-world sailing ambitions "stayed locked up in Cape Verde".

He says he lost his ability to trust people, vital during the challenges on any long yacht voyage.

Even now, he still wonders who Fox really was - that "cool" British guy he once felt so grateful to, whose job advert then turned his life upside down.

He says that he would "really like to see justice done", but has no wish to meet Fox ever again.

"If I meet him, it won’t be me who’s going to talk. It will be another Daniel. All the bad feelings I had in jail will come up and I won’t be able to be a civilised person."

Coming in October World of Secrets, Season 5: Finding Mr Fox.

A joint BBC Africa Eye, BBC Brasil and World of Secrets podcast investigation into a plot to smuggle cocaine valued at more $100m to Europe.