While working on Strength in What Remains, the excruciating and ultimately uplifting story of a survivor of the genocidal conflict in Burundi and Rwanda, Tracy Kidder violated one of his cardinal writing principles. He wrote on airplanes.

"I really can't have someone looking over my shoulder when I'm working," Kidder says during a call to the summer home in Maine that he and his wife, a painter, bought in the 1980s, around the time when The Soul of a New Machine earned him a Pulitzer Prize. "Privacy is a big thing for me."

Usually Kidder has found privacy in what he describes as his uninsulated, "beautifully built little cottage down by a salt water cove" on the couple's property in Maine. Or in the quiet office "with plenty of room for pacing" in their house—an old, converted creamery not far from Northampton, Massachusetts. But over the last five or six years, while he was researching and writing Strength in What Remains, Kidder traveled frequently to college campuses all over the country, where his marvelous account of Dr. Paul Farmer's effort to heal the world, Mountains Beyond Mountains, has inspired enough interest that, as Kidder puts it, "hundreds of schools have inflicted it on their incoming students."

So out of necessity, Kidder learned to write "a little bit" on airplanes.

"Writing is for me, and I suspect for many other people, a way of thinking," Kidder says. "It is the only way that I can begin to make sense of things for myself. So I don't write in a very efficient way. I have to concentrate. The whole idea is to lose myself somewhat, to lose self-consciousness. And when I do that, I feel very vulnerable."

If Kidder feels vulnerable writing under normal circumstances, imagine how he must have felt writing Strength in What Remains, a stunning account of the harrowing journey of a young medical student, Deogratias (Deo), when the horrific civil war between Hutus and Tutsis broke out in Burundi in 1993. It is an amazing journey. Deo witnessed some of the most unimaginable acts of cruelty human beings can commit against one another. He barely escaped death himself. Through luck and the kindness of a schoolmate, he arrived in New York City with $200 in his pocket, not knowing a soul and not speaking English.

Haunted by his nightmarish memories, Deo slept in Central Park and worked for about a dollar an hour delivering groceries while trying to learn English by reading dictionaries in libraries and bookstores. Helped, eventually, by a number of unlikely New Yorkers, Deo entered Columbia University, studied philosophy, went back to medical school and then began working with Dr. Paul Farmer. Eventually he found a healing path for his return to Burundi.

"My wife heard an outline ofhis story and told me about it. The memory of someone else's memory stuck with me," Kidder remembers when asked about the origins of Strength in What Remains. "For me the only hard thing about being a writer is deciding what to do next. My wife said, why don't you go see Deo? I did. And once I heard the story for myself, I thought I had to tell it. Deo is an enormously charming person. Captivating. One feels that even before one knows his story, but the story only enhances that— that a guy could be so good-hearted and so strong that he could return to Burundi and open a clinic, which is really such an instrument of peace. There's a radiance about him."

Kidder spent hours with Deo, dredging up often painful memories, "just talking and talking and talking, and listening really carefully. I'm not a good listener in my regular life, but I'm pretty good when I'm working," Kidder says. Deo was at first a reluctant subject, Kidder says. "I don't blame him. I would never let anybody do what I do to other people. And Deo is, of course, completely publicity shy. There were times when I thought I should stop, and I felt like a real creep for doing this to someone. But once he decided to do it, he did it." In the dramatic finale to the book, Kidder accompanies Deo on a return visit to Burundi and Rwanda.

Kidder lets Deo's story unfold in an unusually affecting double narrative—first as a sort of page-turner, which Kidder says is meant to present "as accurate an account of Deo's memories as I can," and then from a bit of a distance, "to show Deo in the throes of memory." A postscript adds historical context for the chaos and violence unleashed between Hutus and Tutsis in Burundi and Rwanda. But nothing can answer the question Deo seeks to answer when he enrolls in a philosophy course at Columbia: what kind of human being can take up a machete and slaughter his neighbor?

Ultimately, Kidder says, Strength in What Remains is about memory—and forgetting, and taking action. Visiting a genocide memorial site with Deo in Rwanda, he writes that of course we need such memorials. But "too much remembering can be suffocating."

Afflicted by "ungovernable, tormenting memories, Deo first sought solace by studying philosophy at Columbia. But it didn't work."

"I think Deo's solution is not to dwell on memories and not to extinguish them either," Kidder says, "but, rather, to act. The best solution is for him to go back and try to bring public health and medicine to one village. The phrase ‘never again' has clearly become an empty platitude, because genocide keeps happening everywhere. The real answer is remembering, being guided by those memories, and acting."

Growing more reflective Kidder says, "Over the last nine years I've spent the better part of my time with Paul Farmer and Deogratias. They lead you beyond conventional wisdom. A lot of conventional wisdom represents an attempt to ignore the fact that most of humanity is impoverished and in deep misery. These guys and their colleagues are confronting that misery. Through that, I believe another way of looking at the world is bound to arise."

Kidder's Strength in What Remains offers a glimpse of that new world arising.

Alden Mudge writes from Berkeley, California.

With an anthropologist's eye and a novelist's pen, Pulitzer Prize–winning Kidder (Mountains Beyond Mountains) recounts the story of Deo, the Burundian former medical student turned American migr at the center of this strikingly vivid story. Told in flashbacks from Deo's 2006 return visit to Burundi to mid-1990s New York and the Burundi of childhood memory and young adulthood—as the Rwandan genocide spilled across the border following the same inflamed ethnic divisions—then picking up in 2003, when author and subject first meet, Deo's experience is conveyed with a remarkable depth of vision and feeling. Kidder renders his subject with deep yet unfussy fidelity and the conflict with detail and nuance. While the book might recall Dave Eggers's novelized version of a real-life Sudanese refugee's experience in What Is the What, reading this book hardly covers old ground, but enables one to walk in the footsteps of its singular subject and see worlds new and old afresh. This profoundly gripping, hopeful and crucial testament is a work of the utmost skill, sympathy and moral clarity. (Aug.)