My first book was a biography of an obscure American poet born in 1901. When I approached her in 1989, she was living as a recluse in a Florida citrus grove. Fifty years before, she had not merely renounced her own poetry but everybody else’s as well. Through an intermediary, she conveyed to me that I should write a sample chapter (she assigned the topic). If it met with her approval, we would work together on her biography. She could use a secretary, she said.

But before I could reply, she fell ill. When she heard I had proceeded without her, she wrote me angrily, calling me “sluttish.” Her minions sent me lengthy poison-pen missives, dissecting my character. She never read a word of what I’d written. The day after I sent the final manuscript to the publisher, she had a heart attack, as if my book and her life were paired like Siamese twins and I had killed her by finishing it. This is the kind of magical thinking that binds the biographer to her subject.

When I first came upon the archive of the Islamic writer Maryam Jameelah, six years after the attacks of September 11 and in the thick of the American wars in Iraq and Afghanistan, I wasn’t sure what I had found. From the early 1960s until the mid-eighties, Jameelah had written numerous books and pamphlets, translated into a dozen languages. These books were welcomed all over the Islamic world as the definitive word on the superiority of Islamic values over Western ones. Moreover, in mini-biographies of fabled mujahedin, she urged young Muslims to martyr themselves as “freedom fighters” against the godless infidels of the West and their secular Muslim enablers. Her author photo was that of a shapeless black ghost; not even her eyes could be seen behind the dark folds of her veil.

But the Maryam Jameelah archive also contained letters to her parents, Herbert and Myra Marcus, secular Zionist Jews living in a New York City suburb. For Jameelah had been born Margaret Marcus in White Plains in 1934. In 1962 she had left for Pakistan, never to return to America. She went there to live as the adopted daughter of the founding father of militant, political Islam. Her vivid and titillating portrayal of the moral and cultural depravity of America, I then realized, was drawn from Peggy Marcus’s coming-of-age in a postwar suburb, the same one depicted in the best-selling comic memoir Please Don’t Eat the Daisies. The infidels she condemned were her own people.

Yet unlike the hectoring prose of her books, her letters to her parents were affectionate, funny, and acutely observant. Filled with dramatic incident, dialogue, and surprise developments, there were pages and pages of mesmerizing details about living in purdah under the roof of the aging mullah who was the first to call for a twentieth-century global jihad.

I was well into writing her story when I came upon a drawing she’d done dated September 11, 2001, forty years after she had left America. Even then I was not prepared to consider the possibility that Maryam Jameelah might still be alive. Was I obliged to meet her? I had her letters and writings, what more could she add? What need did I have of an old woman with unreliable memories living on the other side of the world?

But if she lived to see the attacks, what did she make of them? Did she watch the city she had once known so well fall to pieces? Had she changed her mind about the evils of the West or did she remain resolute? Could she help me make sense of 9/11 and the war on terror that followed, or would she see me as her sworn enemy? Suddenly, the obscure story of Margaret Marcus and Maryam Jameelah became the means by which I might cut the Gordian knot that bound America and Islam in enmity.

At one level I knew this was yet another example of magical thinking. But in the long and largely lonely years spent writing a book, all sorts of absurd ideas keep you company. So I wrote a letter to the address of her publisher and Maryam Jameelah promptly wrote back, inviting me to come see her in Pakistan. I arrived six months later, in December 2007, at the height of the state of emergency.

As soon as I stepped into her room, I realized that the woman I had conjured from the letters bore little resemblance to the woman in front of me. While she talked non-stop in a strange keening voice I tried to remember what it was I had wanted from her. Her third-floor bedroom was suffocating; as soon as I arrived, I couldn’t wait to leave and no sooner had I left then I realized that I had to go back. As if I had forgotten something. This kept up for two weeks. I still can’t fully explain what happened to me in that room. But then Benazir Bhutto was assassinated, and with that the nuances of the argument between Islam and America and the details of the dueling narratives of Margaret and Maryam seemed pretty much beside the point. I returned to New York shattered.

Eventually, I reconceived the entire book, stretching the art of biography to accommodate both the facts and the fantasies Maryam and Margaret had spun in those letters to her family. For she, too, had struggled to make sense of the mystery of her life. She had cast and recast the signature events of the twentieth century in a way that made the radical turn she had taken defensible, romantic, even noble. By portraying that struggle both in her words and in my own, I hoped to get beyond the supposed divide between our respective, warring worlds.

And when I tore open her long-awaited letter it seemed at first to promise a kind of truce: “This note is to acknowledge safe receipt of your book parcel from Delhi (India). I am satisfied with your book as a fair and just detailed appraisal of my life and work.” Not a week later, however, the library in which I found her archive also received a letter. In this one, Maryam Jameelah insisted my portrayal of her was filled with falsehoods and unfounded allegations.

Perhaps I could capture only a hint of that woman beneath the veil. Perhaps fifty years of purdah limited her view of herself and the world she had a hand in making. But somewhere between these two letters lay the unearthly promise of biography: a glimpse of truth, the small window of understanding.

Deborah Baker’s most recent biography is The Convert: A Tale of Exile and Extremism. She lives in New York and India.