Peter’s Coffee Shop in Dandong, China, looks like the hundreds of other “Western” cafes scattered across the country: It offers a menu consisting of burgers and other comfort food, and advertises regular sessions where Chinese locals can practice their English with foreign guests.

But the cafe has now attracted attention for the wrong reason. Xinhua reported that its proprietors, a Canadian couple named Kevin and Julia Dawn Garratt, are under investigation for nothing less than espionage, suspected of stealing state secrets about China’s military and defense research. The Garratts’ whereabouts are currently unknown; they may have been detained, but China’s Foreign Ministry claimed that their “various rights were fully guaranteed.”

Although the Chinese government frequently accuses Western countries, especially the United States, of cyber-espionage, arrests of individuals who fit the profile of the Garratts are unusual. But a closer look at the details of the couple’s lives in China provide clues into why they attracted the scrutiny of the Chinese government.

The Garratts made no secret of their evangelical Christianity; according to a frequent visitor to Peter’s Coffee House quoted by Reuters, the cafe served as a meeting point for Dandong’s foreign Christian population and regularly played religious-themed music. And in a sermon delivered in November 2013 at the Terra Nova church in Surrey, British Columbia, and posted on the church website, Kevin Garratt tied his Chinese business to explicitly religious themes.

“God gave us a vision a number of years ago, and that vision was to go to a little place called Dandong, a little city of 800,000 people on the border of China and North Korea. And God said start a business, start a coffee house,” he said.

Proselytizing remains illegal in the People’s Republic of China, which officially adopted atheism upon the country’s founding in 1949, and people suspected of being Christian missionaries are occasionally expelled from the country: Most recently, China ejected nearly 100, in 2007. But China is also home to a vibrant Christian population of more than 70 million people, many of whom worshipping in “underground churches” that Beijing largely tolerates. Christianity, alongside Buddhism, Taoism and Islam, is now recognized as one of the few permitted religions in China.

The Garratts’ connection to North Korea may ultimately prove more damning than their Christianity. Dandong is located on the Yalu River, which forms the Chinese-North Korean border. North Koreans frequently flee to the city and its surrounding countryside in search of economic opportunity, and at great personal risk: Those who escape the North Korean armed patrols and are caught by Chinese officials cannot claim asylum and are immediately repatriated. Dandong serves as a base for Christian organizations who work with North Korean refugees.

One Christian who spent time in Dandong is Kenneth Bae, a Korean-American arrested by North Korea in 2013 and sentenced to 15 years in prison on charges of “attempting to overthrow the North Korean government.” The Chinese government, for its part, has yet to charge the Garratts with a specific crime, and their son Peter -- the namesake of the coffee house -- denies that they did anything wrong.

Nevertheless, the investigation into the Garratts offers a fresh reminder that China’s long-standing sensitivity toward its border regions remains very much intact.