The heir apparent to China’s leadership as of Tuesday had not been seen in public since Sept. 1. He went missing at a sensitive moment. The 18th Congress of the Communist Party, which is expected to elevate him to the top position of general secretary, is due to be held within weeks — though, curiously, no date has been announced. Scandals involving party leaders — including the alleged murder of a British businessman by the spouse of one boss and a fatal Ferrari crash by the son of another — have raised questions about whether the carefully orchestrated transition is off-track. Mr. Xi canceled meetings with four foreign leaders in a week, including Secretary of State Hillary Rodham Clinton and the Danish prime minister, with no explanation.

Maybe Mr. Xi merely strained his back, as one rumor has it, or had a mild heart attack, as another contends. The fact that China’s citizens and the world were left to wonder is yet more evidence that the country’s creaky Stalinist political system is entirely unprepared to meet the challenges it faces — from a slowing economy to a booming social Internet.

Neither Mr. Xi, expected to replace Hu Jintao, nor Li Keqiang, who is to step in for Wen Jiabao as prime minister, would likely stand up well to uncensored scrutiny. According to reporting by Bloomberg News, Mr. Xi’s extended family has amassed stakes in companies worth hundreds of millions of dollars as well as seven properties in Hong Kong valued at $55 million. Mr. Li, according to a report in the Financial Times, has had an administrative career “short on achievements and long on disastrous events,” including the coverup of an AIDS epidemic caused by infected blood.

All the same, Beijing’s policy of trying to keep secret even the most basic information about Communist Party leaders, a practice pioneered a century ago in the Soviet Union, is unsustainable. More than 300 million Chinese now have social media accounts, and an army of government censors is unable to stem rumors about Mr. Xi’s disappearance or complaints about the lack of official information. In the vacuum, sensational stories are circulating, including a claim that Mr. Xi was targeted in a car crash by an associate of recently deposed Politburo member Bo Xilai.

Assuming that Mr. Xi returns and takes office as planned, the pressure he faces for transparency and accountability will only grow. China appears headed for a significant economic slowdown, which means more dissatisfied citizens and less tolerance for governmental incompetence and corruption. If they are wise, Mr. Xi and Mr. Li will open the political system rather than allowing it to crumble around them. A good first step would be to tell the truth about their own activities.