The title of Rebecca Donner’s astonishing new book is a line by Goethe, from a volume of his poems that had been smuggled into the cell of Mildred Harnack — an American woman who was shackled in a Berlin prison, awaiting her death sentence by the Nazi regime. On Feb. 16, 1943, the day she would be taken to the execution shed and beheaded, a chaplain found Mildred hunched over the poems, scribbling in the margins. The heavy gothic font of the German original was accompanied by the ghostly script of her English translation, written with a pencil stub.

Donner includes an image of that page in “All the Frequent Troubles of Our Days,” a book about Harnack’s life and death that turns out to be wilder and more expansive than a standard-issue biography. (A diligently researched book about Harnack was published two decades ago, by Shareen Blair Brysac, titled “Resisting Hitler.”) Donner is Harnack’s great-great-niece, so this is a family history too. It is also a story of code names and dead drops, a real-life thriller with a cruel ending — not to mention an account of Hitler’s ascent from attention-seeking buffoon to genocidal Führer.

Mildred Fish was born in Milwaukee in 1902; her husband, Arvid Harnack, was German. They met as graduate students at the University of Wisconsin, and eventually settled in Berlin. After Hitler was appointed chancellor in 1933, they started holding secret meetings in their apartment for underground resisters. Mildred was teaching English and found recruits among her impoverished students; by 1935, Arvid had landed a job at the Ministry of Economics, where he was privy to intelligence that he would eventually give to the Soviets. Whether this fateful decision had to do with antifascist expedience or pro-Communist ideology — the Nazis would later call the espionage group Red Orchestra — Donner doesn’t quite decide.

Donner pieces together Mildred’s life from fragments, sifting through government archives, interviews, photographs, diaries and letters — though some of those diaries and letters were destroyed, and the most personal items weren’t always revealing. “Her aim was self-erasure,” Donner writes; such effacement was a matter of survival. Several letters show Mildred trying to present a brave face for her worried family back in the United States. Staying meant risking imprisonment and perhaps death; leaving would have meant abandoning Germany to the Nazis. Even at the end of this extraordinarily intimate book, Mildred remains somewhat of an enigma. “Despite her wish to remain invisible,” Donner writes, “she left a trail for us to follow.”

What emerges is a portrait of a woman who had already noticed how economic suffering was tearing the fractious Weimar Republic apart. When establishment conservatives pushed for Hitler’s appointment as chancellor, he had been widely derided as too bumbling and ludicrous to ever obtain any real power. “All feel the menace but many hide their heads in the sand,” Harnack wrote to her mother in 1932. Donner evokes a Berlin on the brink, teeming with linden blossoms and swastikas.