An anonymous letter calling on President Xi Jinping to resign for the good of China and his own safety seemed to be digital rumor-mongering when it appeared on the Internet this month. It spread by email and lingered on a small domestic Chinese news site before it was removed. But the response from Beijing has been anything but dismissive.

Surprising even some hardened critics, Mr. Xi’s security forces have overseen a far-reaching inquisition to root out the culprits behind the letter, resorting to measures that have drawn more attention than the letter itself. They have detained at least 11 people, including relatives in China of two exiled writers accused of spreading or promoting the letter. READ MORE