In Poland today, having worked for the secret police is a heavy thing to admit. The Ministry of Public Security played a crucial role in imposing Communist Party rule by force after the World War II. Its members jailed the opposition and silenced critics. To establish its dominance, the Communist Party fought what amounted to a low-level civil war against the vestiges of the non-Communist resistance. The Ministry of Public Security was the hard edge of Communist power in Poland. In its role as a counterintelligence organization, it also engaged in a shadow war with the C.I.A. and other Western spy agencies. And it’s in this role that my grandfather’s story reappears in the files.

Most of what I know about his life after his career as a partisan comes from a Communist Party personnel file, which I decided to request from the Polish Institute of National Remembrance after finding a tantalizing mention of my grandfather’s postwar life in another one of the institute’s publications. But the file is vague on what he was doing in those years. It simply lists the departments he was posted to: the department for fighting counterrevolution; counterintelligence; countersabotage. Now it becomes necessary to follow him through the footnotes of historians who study intelligence operations during the start of the Cold War.

In 1950, he turns up as a case officer involved in something called Operation Caesar. Operation Caesar was a false-flag operation, in which the Polish secret police rounded up members of a real, underground resistance group and persuaded them to switch sides. Then they sent them across the Iron Curtain to the West. In the guise of a real resistance movement, they received money and matériel from the C.I.A. and MI6 — over $1 million, and several hundred pounds of gold in total — then turned around and passed those on to their Polish handlers. My grandfather, it seems, was one of those handlers.

What happened next is difficult to say. He died in 1963, when my mother was 7. She didn’t know him well. What memories I’ve heard from that time are fragments. He played tennis. He read books. He announced his engagement to my grandmother by saying to his sister, “Jadzia, I’m getting married. Let me have a shirt.” In fact, the best source of information on his life is the file, which we obtained only last year. Even so, much is unsaid.

His story fits into a pattern. My grandfather belonged to a generation of Polish Jews that grew up with the revolution and put all their faith in it. If they survived long enough, they lived to see that faith betrayed.

For Polish Jews in the 1920s and ’30s, joining the Communist movement represented the “most radical of all possible rebellions,” in the words of the Swedish sociologist Jaff Schatz, who wrote the defining work on this generation. It was a rebellion against one’s parents and the traditions of Jewish life. It also meant participating in an illegal organization, which brought with it the constant possibility of imprisonment.

To the members of my grandfather’s generation, Communism was a way to be modern and a way to escape the shtetl. It was a way to fight anti-Semitism and oppose fascism, both in Poland and worldwide. And perhaps most important, it was way to build the future and be a part of something larger than themselves. Being a Communist was a life of total commitment, persecution and permanent insecurity. But becoming a Communist also meant an intense sense of participation in the movement of history and in the revolutionary upheaval of the world. That upheaval would come soon enough — just not in the way they expected.