Photo by Suo Takekuma / Pool / Getty Images Within days of being appointed China’s foreign minister in December, Qin Gang had embarked on a week-long tour of Africa. The career diplomat, who had previously served as ambassador to the US and was known as a shrewd political operator who could be both charming and combative, adopted a hectic schedule. He jetted around the world pressing China’s interests as one of the country’s most prominent envoys, and appeared to be a rising star. But then Qin disappeared. The 57-year-old has not been seen in public since 25 June, when he...