When Lin Biao, China’s then heir apparent, died in an air crash more than 40 years ago, it took the Communist Party two months to inform the public.

This week’s unexplained disappearance of Xi Jinping, China’s leader-in-waiting, who has not been seen in public for 11 days, shows that, despite the country’s economic transformation, when it comes to its leaders, Beijing is as secretive now as it was in 1971, when Lin Biao died and Mao Zedong was still in power.

According to Beijing’s official version, Lin had been plotting a coup against Mao and decided to flee to the Soviet Union with his family after learning that he had been found out. His flight crashed in Mongolia, killing everyone on board. While Russian forensic evidence confirmed that he died in the crash, foreign historians continue to doubt Beijing’s explanation of a coup....