Kevin and Julia Garratt on their experience as detainees in China

Canadian couple Kevin and Julia Garratt were detained in China in 2014 and accused of spying. Amid an escalating feud between Canada and China and allegations of retaliatory detentions, the pair tells the BBC about what it was like - and how they ever made it home.

Kevin Garratt remembers well the night he and Julia were arrested in north-eastern China.

He recalls being pulled away from his wife as they walked through a restaurant's downstairs lobby, and pushed into the back of a black sedan filled with burly officers.

He thought the whole thing was some terrible mistake.

Julia, forced into a separate sedan, found herself shaking in fear and shock at the sudden turn of events, and the drive in the darkness.

She thought: "This is going to be my last night.

"I don't think I've ever felt that level of fear and panic before. And also just sad for my family and my children, because there was no warning, there would be no chance to say goodbye."

The Garratts had lived in China since 1984, and from 2008 operated a coffee house popular with Western expats and tourists in Dandong, a city on the North Korean border, while continuing to carry out Christian aid work.

But unbeknownst to either of them, early in 2014 and thousands of miles away, American authorities were launching a crackdown on Chinese cyber-espionage. One of the men in their sights was Su Bin, a Chinese resident working in Canada.

That June, Canadian authorities picked up Su, accused of stealing data about military projects and selling it to China, for extradition to the US.

While China has denied it, Canadian officials and observers believed the Garratts' arrest was a tit-for-tat detention and an attempt to pressure Canada for Su's release.

Canada's ambassador in Beijing at the time, Guy Saint-Jacques, describes them as "a couple of Canadian missionaries who had been in China 30 years doing good work".

He tells the BBC their arrest "was the first case where we saw a clear retaliation for something that had happened in Canada".

When he met counterparts at the foreign ministry about the case, Saint-Jacques recalls: "They never said directly 'let's do a swap.' But it was very clear what they wanted."

On the night of the Garratts' arrest - the beginning of months of detention for the pair - they had been invited for dinner by a friend of a friend, who told the couple they wanted to talk about their daughter going to study in Canada.

But something about the dinner felt strange.

"It didn't seem genuine, and the daughter never came," Kevin says.

Julia says it was only later they realised the whole evening had been a set-up for their arrest.

"It was very carefully thought through and planned in advance. We had no idea," she says.

Parts of the couple's story could be pulled directly from today's headlines.

In December, Chinese telecoms executive Meng Wanzhou, 46, was detained in Vancouver for allegedly breaking US sanctions against Iran.

This week, the US filed charges against Huawei and Meng, and the US is seeking her extradition. Both Huawei and Meng have rejected the allegations.

Following Meng's arrest came threats of "grave consequences" from China if the tech heiress and chief finance officer at Huawei, China's largest private company, was not released.

In mid-December, two Canadian men - former diplomat Michael Kovrig and businessman Michael Spavor - were held in China on accusations of harming national security.

Like in the Garratts' case, their detention is seen by many China analysts as a reprisal.

The Garratts' experience in detention parallels what Canadian officials and others have suggested that Kovrig and Spavor are living through - daily interrogations, being kept in a room with lights on day and night.

"I don't know what they did or didn't do, but I know what they're going through right now," says Julia.

The Garratts say they were never physically harmed but were watched by guards around the clock, and had to request the most basic necessities when they needed them.

"You want a drink of water, they have to go get it for it. Brush your teeth, they get it for you. It's really meant to frighten and control you," says Kevin.

Julia says the first few nights, she put a blanket over her eyes to block the light, but the guard pulled it down.

"I thought: 'That's a rule, I can't cover my face to sleep in the dark, they need the lights shining in my face.' They had very strict protocol."

They also experienced daily interrogations for up to six hours.

Tit for tat arrests

Their interrogators had a decade of details about their time in China and their travels, and asked over and over about the minutia of their activities - the why, the when, and the where. Whom they met.

"They would ask the same questions two month later and compare the answers," says Julia. "It's very, very gruelling."

Some four years later, they have documented their experience in a book, Two Tears on the Window, published in November.

Devout Christians, they say prayer and the support of both their close family and the wider church community helped them through their time in detention.

"I had the sense that my peace cannot be stolen from me, my true freedom cannot be stolen from me. And I think there was great comfort in that," says Julia.

She was released on bail in February 2015, pending trial. In January 2016, still in detention, Kevin was charged with stealing state secrets.

A month later, Su waived extradition and headed to the US, where in March he pleaded guilty to hacking into major US defence contractors, stealing sensitive military data and sending it to China.

Saint-Jacques says that Chinese officials seemed taken by surprise by Su's decision to cut a deal with American officials.

He believes that turn of events, combined with a visit to China by Justin Trudeau, during which the newly elected PM raised Kevin's case, were instrumental in securing Kevin's release.

He was deported to Canada in September 2016 after 775 days in detention, and reunited with Julia, who had left the country earlier that year.

Meanwhile, Meng's case continues to strain China's ties with Canada and the US.

Chinese officials have called her arrest a "serious mistake", accusing Canada of double standards and "Western egotism and white supremacy".

She is out on bail and under house arrest in Vancouver, where she owns property. She is next due in court on 6 March, but the case could possibly drag on for years.

It also comes amid growing scrutiny in Western countries over Huawei, which is a world leader in telecoms infrastructure, in particular the next generation of mobile phone networks, known as 5G.

Concern about the security of the company's technology has been growing, particularly in the US, UK, Canada, Australia and Germany, which fear its products could be used for spying, an allegation which Huawei denies.

Amid the diplomatic dispute, Canada has worked to rally international allies to its corner.

Earlier this month, over 140 diplomats - including Saint-Jacques - and academics signed an open letter to President Xi Jinping calling for the release of Kovrig and Spavor.

Canada also fired ambassador John McCallum on Sunday following controversial comments he made about Meng's extradition case.

For the Garratts, despite the international significance of cases such as theirs, it's important to remember that individuals and their families have got caught up in the dispute.

"The human cost is huge. That's the largest cost that's paid by the individuals that are directly implicated, unjustly implicated by these big things," she says.