It's 1975, Lithuania. You receive a letter in the mail—brief, and on KGB letterhead. "You are invited to a friendly chat at our headquarters," it says. "Next Monday, 10 a.m." Gulp. These "chats"—frequent occurrences in Khrushchev-era Lithuania, Latvia, and Estonia—are the current fascination of Obermann Fellow-in-Residence Edward Cohn. A professor of history at Grinnell College, Dr. Cohn...