Second-guessing life-or-death decisions with the hindsight of history is only natural, asserts British journalist Daniel Finkelstein in his unflinching and gripping family history “Two Roads Home: Hitler, Stalin and the Miraculous Survival of My Family.” But even the best guesses available to Jews, like his grandparents, seeking to escape Nazi Germany and Poland in the 1930s could not have forecast the devastatingly swift onslaught of broken promises and Axis military strikes that would so quickly result in the occupation of Allied countries, which were only a short time before considered “safe” from Hitler’s antisemitic persecution.

The margin of error for prediction had been further tightened by the severe immigration quotas that Britain, the United States and other countries imposed to limit if not bar Jewish arrivals to their shores. That indifference was based at least in part on prejudice, epitomized by the refusal to ease border restrictions by 31 of the 32 governments represented at the 1938 on the plight of German Jewish refugees. (The exception was the Dominican Republic.) The result, Finkelstein writes, is that “fleeing would not have been enough; the flight would have needed to be to the right place. And the right place was unknowable.” Even to those who, like Finkelstein’s German-born grandfather, the journalist and scholar Alfred Wiener, had begun loudly warning the public about Adolf Hitler’s intentions as early as the 1920s.

The fact that Finkelstein is here to tell his tale assures us that his immediate forebears ultimately would succeed in finding roads back to life, even if not to the remembered places that they had once called home. That does not prepare us, however, for the harrowing struggles and relentless degradations they confronted during their respective ordeals: the disease, starvation and imminent death threats endured by his German-born mother’s family in Hitler’s death camps, and the parallel horrors and deprivations withstood by his father’s Polish family in Joseph Stalin’s slave labor sites in the Siberian Gulag.

Although Finkelstein seldom wavers in his crisp recounting of this monstrous travelogue, I periodically needed to pause to take in the cruelties so routinely perpetrated by both Hitler’s and Stalin’s forces on the vast millions of prisoners across Europe whose relative luck in the long-shot odds of survival had as little chance as, or less than, the Finkelsteins’. What kept me reading was not only the book’s nail-biting pace — more than that, Finkelstein’s adroit depiction of the individual character and sensibility of each member of his extended family makes us connect with and care about their fates.

The first family scion we meet is Wiener, a proud German patriot and Jew who had returned from his World War I military service fighting for Kaiser Wilhelm II with a chilling apprehension: that vast numbers of disillusioned veterans embittered by defeat, and already primed by radical right-wing parties to blame the Jews, would result in “a mighty antisemitic storm.” He soon became the outspoken leader of the Central Association of German Citizens of the Jewish Faith, focusing in particular on Nazi antisemitic threats.

Within months of Hitler becoming German chancellor in 1933, Wiener and his wife, Grete, and their three young daughters (Ruth, Eva and Mirjam, Finkelstein’s mother) moved from their Berlin home to Amsterdam, where Otto and Edith Frank and their daughters Margot and future diarist Anne, who had fled from Frankfurt, were neighbors. Counting on Holland’s neutrality, Wiener and Grete (who had earned a PhD in economics) ran what Finkelstein describes as “the world’s most important” center of anti-Nazi research, combating Hitler by circulating worldwide news of his increasingly brazen persecution of the Jews and aggressive threats and claims to non-German territories. But in 1939, pressured by Dutch fears that his operation would antagonize Hitler, Wiener moved his organization to London and then New York, leaving the rest of his family behind while he attempted to obtain visas for them. But timing is everything. Approval of their papers arrived on the same day that Germany invaded Holland. They would remain trapped under Nazi rule, imprisoned and endangered at different concentration camps for the war’s duration. Wiener would be reunited with his daughters in 1945, but despite numerous attempts to save them all, he would never see his wife again.

Meanwhile, in the eastern Polish city of Lwów (now part of Ukraine and called Lviv), the former Polish army officer and wealthy steel manufacturer Dolu Finkelstein had only recently moved with his wife, Lusia, and their only child, Ludwik (who would become the author’s father), to a stylish new house in the most prominent neighborhood in town when, just days after Germany’s September 1939 invasion of Poland from the west, Stalin attacked Poland from the east — and, in keeping with his secret pact with Hitler to divide the country between them, occupied their city, with Soviet commander Nikita Khrushchev in charge. In short order, the family fortune and properties were confiscated, and the family members themselves separated and deported to different destinations: Lusia and Ludwik to Kazakhstan, Dolu to Siberia.

Finkelstein tracks each family member’s physical passage through the inferno alongside the soul-scarring cycles of doubt and despair to arrive at something like resolve and even hope. In this way, he also illuminates a major key to their resilience — the intense web of mutual affection and concern that propelled an inner determination to persevere for each other, even when their own strength waned. In presenting the testimony of two families who witnessed and endured despite the odds, Finkelstein has written an indelible chronicle of both historical and personal significance.