Retired Chinese official Li Chuanliang was recuperating from cancer on a Korean resort island when he got an urgent call: Don’t return to China, a friend warned. You’re now a fugitive.

Days later, a stranger snapped a photo of Li in a cafe. Terrified South Korea would send him back, Li fled, flew to the U.S. on a tourist visa and applied for asylum. But even there — in New York, in California, deep in the Texas desert — the Chinese government continued to hunt him down with the help of surveillance technology.