But it was more than that. These men sat at the top of the British intelligence and diplomatic corps. The nation’s faith in its political and academic elites was permanently shaken, and the partnership between the US and UK spy agencies became a minefield of distrust and paranoia at the very moment that the West needed a united front more than ever.

Needless to say, this rich ground has been thoroughly plowed by historians and novelists alike over the years, and many a spy thriller owes its inspiration—directly or indirectly—to one or more of the Cambridge Five. But as I dug deeper into these men and their lives, I was less fascinated by the mechanics of espionage—the what and the how of what they did, the narrow escapes and unspeakable blunders—than by the who and the why. How could these intellectually brilliant men cling so willfully and catastrophically to their beliefs, even as the everyday evils of the Soviet state lay so plain before them? How could they betray their friends with such cold disregard? Consign women and men to their deaths without a second thought? How did this constant betrayal and secrecy affect them psychologically? And my God, what did it do to their families? The wives and children who bore the brunt of their inner torment? Were they unwilling passengers or fellow travelers?

These questions brought me to the marriage of Donald and Melinda Maclean, a fraught and complex partnership if ever there was one. At various points in their relationship, Melinda was his victim and his enabler, sometimes fed up and other times addicted, and easily the steelier of the two. Because the intelligence service dismissed her as a brainless housewife, she was able to facilitate Maclean’s defection in 1951 while eight and a half months pregnant, then slip away to join him with the children two years later. It hit me that the spymasters and spy catchers on both sides were missing a trick or two, and this kernel of inspiration grew and transformed into Our Woman in Moscow.

Sasha bears a physical and psychological resemblance to Maclean, and certain scenes are inspired by real-life incidents that marked Maclean’s deterioration into alcoholism and self-loathing—the farce on the Isle of Wight, for example, is roughly drawn from a disastrous picnic expedition on the Nile during Maclean’s posting to the British embassy in Cairo. Despite these parallels, Sasha and Iris are fictional characters and the narrative itself arises from my own imagination. Maclean died of natural causes in the Soviet Union in 1983; Melinda returned to the United States permanently in 1979, though not before having had an affair with Kim Philby, who defected in 1963.