The strange sound came at night: a crack like a marble striking the floor of the apartment above them.
Mark Lenzi and his wife had lightheadedness, sleep issues and headaches, and their children were waking up with bloody noses — symptoms they thought might be from the smog in Guangzhou, China, where Lenzi worked for the State Department. But air pollution could not explain his sudden memory loss, including forgetting names of work tools.
What began as strange sounds and symptoms among more than a dozen U.S. officials and their family members in China in 2018 has turned into a diplomatic mystery spanning multiple countries and involving speculation about secret high-tech weapons and foreign attacks.