During 26 years at the CIA, Marc Polymeropoulos spent a lot of time in rough places, like war zones in Iraq and Afghanistan. But he never suffered any harm until December 2017, when he was sound asleep at a Marriott Hotel in Moscow near the U.S. Embassy. "I was awoken in the middle of the night," recalled Polymeropoulos, 51. "I just had incredible vertigo, dizziness. I wanted to throw up. The room was spinning. I couldn't even stand up without falling down. I had tinnitus ringing in my ears." He suspected a bad case of food poisoning and carried on...