David was uniquely able to draw the connections between the human and historical, the personal and political, pulling on the seamless thread that is the human condition. He adopted language and techniques that appeared simple — often reducing politically significant and complicated matters to a choice faced by an individual — but were actually rather complex. With his words, the dark recesses of our modern world, and the choices we face, touched readers in a manner they — we — felt to be deeply personal.

David got his start in the world of espionage; he would later draw on the personal experience of working for the intelligence services in Germany. His third novel, “The Spy Who Came In From the Cold,” was his first best seller. It was a simple tale of a British agent using dubious means to promote supposedly democratic values. “Are you a spy,” another protagonist would be asked two decades later, in “A Perfect Spy,” or “merely a criminal?”

Distrust was a fine thing for us, the lawyer and skeptical former spook. Our friendship soon grew beyond our early gulf war conversations. One day, he asked if I might be willing to review a draft of his next book; it was a means of peering more deeply into his characters, this time lawyers. He wanted a check on fashion and speech. This became a joyful routine, David at my front door, arms thrust forward with the text of a new book.

I became a different type of reader, immersed in his style and forensic attention to particulars, recognizing how matters of structure and form were harnessed to bring the reader to the heart of a dilemma, as yet another decent human called upon to act with unspeakable duplicity. The lens usually had something to do with spies, but not always, and over the years he went back and forth in time. In 2017, he even brought back George Smiley, the most famous of his characters, in “A Legacy of Spies." Fifty-six years after his first appearance, Smiley was called upon to address the decline of Britain and the mendacities of Brexit.

Over time, my own writing on the origins of genocide and other international crimes in the years of the Nuremberg trial connected unexpectedly to matters of espionage. Looking into the murky world of the Nazi escape route from Europe to South America, known as the ratline, I turned to my neighbor for insights into the postwar years. I wanted to understand how could it possibly be that senior SS officers came to be recruited by the Americans, so soon after the war’s end.