I've been waiting for weeks for this call, which comes unexpectedly one afternoon as I'm heading home in a taxi from Beijing Airport. I'm told to change direction and go to the Beijing Rail Station. Moments later, my mobile phone rings again, and I'm told to proceed to the lobby of the International Hotel. But the plan changes again, and I'm instructed to wait in front of the Friendship Store.
A taxi pulls up shortly after I get there and someone shouts for me to get in. I jump into the taxi next to two very nervous North Korean teenagers.
In about an hour, the refugees hope to board a train bound for freedom. The plan is to make it past Chinese security into a foreign consulate in another city, where it's hoped security will not be as vigilant as in the capital.
At the train station, we meet two other teenagers, accompanied by a foreign missionary and an ethnic Korean Christian from northeast China.
The two boys and two girls, aged 15 to 17, who sneaked into China during the past four years, are so anxious they can barely hold back tears.
They say they were adopted by ethnic Korean and Chinese Christian families on the mainland, and later converted to Christianity. They decline to answer questions about their natural or adopted families, but freely describe the poverty of their lives in North Korea and China.
One of the boys, however, boasts that he didn't have it so bad. 'When I was in North Korea, I had corn meal three times a day,' 15-year-old Choe Il says, possibly not realising that three dollops of corn meal a day is not standard fare in most countries.
Im Eun-hong, 17, who only completed grade four, says: 'In North Korea, I ate congee three times a day. I rarely ate meat.'
She crossed the border and walked for two days, and survived by begging food from peasants and sleeping in the woods to avoid being seen. 'I'm very afraid,' she says, adding that she hopes to eventually go to the US, 'to make money and to survive'.
It took Kim Guang-il, 17, who has only had two years of schooling, a day of walking to get into China. 'Friends told me I could make money in China.' He sold wood for a living, and says he wants to become a computer engineer.
Kim Eun-ok, 17, crossed the Tumen River in daylight in 2000 to look for her younger sister, who is now in South Korea. 'I desperately wanted to come to China,' she says, adding, however, that 'my life is very bitter here'.
The next day, the missionary, who discovered the four hiding in Harbin, calls me and says he watched the teenagers walk past guards into the British consulate in Shanghai, apparently using forged South Korean passports.
He says one of the girls called him moments later from inside the compound, crying as she described how an alert Chinese guard attempted to pull them out just after they got inside the consulate grounds, but the guard retreated when a British official intervened.
Days later, a British Embassy spokesman told me that the four teenagers had already left China. He refused to say where.
I have since learned the four made it to South Korea, and underwent weeks of reorientation before starting their new lives.