In 1933, after Hitler and the Nazi Party consolidated power in Germany, Immanuel Birnbaum, a German-Jewish journalist based in Warsaw, is forbidden from writing for newspapers in his homeland. 6 years later, just months before the German invasion of Poland that ignites World War II, Immanuel escapes to Sweden with his wife and two young sons. Living as a refugee in Stockholm, Immanuel continues to write, contributing articles to a liberal Swiss newspaper under the name Dr. B. He becomes increasingly entangled with British intelligence agents. But when the Swedish postal service picks up a letter written in invisible ink, clearly by Dr. B. himself, the Allied plotters are exposed. But could a Jew living in exile and targeted for death by the Nazis have wanted to tip them off?