Matthiessen and I sat in his office in the back, talking about “In Paradise,” his new novel. “It was a very odd book and a very difficult book for me to do,” he said. I wondered why, at this stage in his life, he had stuck with it. His legacy is secure, and he has said in numerous places that he thinks most writers don’t know when to quit, that very few do quality work after they get beyond a certain age. “I couldn’t walk away from it,” he said. He stopped for a moment. “It was such a powerful experience, and I just couldn’t walk away from it. I tried.”

The experience was a retreat at Auschwitz in 1996, led by Glassman, who appears in the novel under the transparent designation of “Ben Lama.” The retreatants, who came from all over the globe, sat in meditation on the train platforms in Birkenau where people had been sorted and selected for death. In the evenings, after the sittings, everybody would gather to talk about the day’s experiences. One night, there was a spontaneous outburst of dancing, which was deeply moving for some and outrageous to others. “How does that happen?” Matthiessen asked me rhetorically, posing the question of the novel. He referred back to the novel’s epigraph, a poem by Anna Akhmatova that wonders, when we are surrounded by so much death, “Why then do we not despair?” Matthiessen looked at me, eyes dancing, beating on his leg in time as he said, “Something, something, something,” unable to name the mysterious life force that allows us to rejoice even at Auschwitz. “That fascinates me.”

On another night during the retreat, Matthiessen stood up to speak. “It was a very charged atmosphere,” Glassman told me, “and he was very passionate when he was talking. He got up and said — I remember so distinctly — that man is basically an evil being.” As Matthiessen remembers it, “I just got up and made a generality that if we think the Germans are unique in this regard, we’re crazy. We’re all capable of this, if the right buttons are pressed. Our countries have all done it. Man has been a murderer forever.” But then he cautioned me to take the drama out of it. “It was no great manifesto up there. I just wanted to say, ‘Come on, we’re all in this together.’ ”

The novel that emerged from Matthiessen’s experiences at Auschwitz is short and stark, narrated by a middle-aged academic named Olin Clements who blunders his way through the entire book. The settings are Krakow and Auschwitz; what little nature there is in the book is bleak, windy and covered in snow. “I felt like I was cold and damp the entire time I was reading the book,” said Becky Saletan, Matthiessen’s editor at Riverhead Books — maybe not the greatest recommendation for the reading experience, yet exactly how Matthiessen wants you to feel. The book is a continuous unresolved argument, between retreatants and inside the mind of the narrator. The few moments of uplift, like the spontaneous outbreak of dancing, are quickly splintered by disagreement.

Olin is not unusual as a fictional character for Matthiessen; many of his subjects are strangers to themselves, acting for reasons they don’t understand, out of some vague impulse to find a “home” that is more an idea than a place they can ever actually return to. In his own life, Matthiessen found a home in Zen. As he writes in “The Snow Leopard”: “In the longing that starts one on the path is a kind of homesickness, and some way, on this journey, I have started home. Homegoing is the purpose of my practice.” And yet, in “In Paradise,” Matthiessen takes even that consolation away. The evil that Olin encounters at Auschwitz is so terrifying that spiritual practice can’t mitigate it. Olin reflects on Solzhenitsyn’s observation that “the line dividing good and evil cuts through the heart of every human being,” and then decides to show it to one of the retreat leaders — who responds with a Buddhist bromide about eliminating “all self-lacerating partial truths while good and evil fall away.” It is correct doctrine, but Matthiessen makes it sound like claptrap. Of spiritual practice in general, with which he has a casual and conflicted relationship, Olin wonders: “How long would such delicate attainments have withstood the death camp’s horrors?” It is another way of asking the question we all ask of ourselves: How would I have fared?

The book is grim, but Matthiessen isn’t. Earlier that morning, I watched as he said goodbye to a guest who stayed over the previous night. They were business associates, friendly but maybe not friends, and as the guest was at the door, he good-naturedly offered optimistic advice about radical experimental measures that Matthiessen might take. Matthiessen smiled and said: “I don’t want to hang on to life quite that hard. It’s part of my Zen training.” In preparing for our interviews, having read “In Paradise,” I wondered whether the Buddhist teachings were providing him any more consolation than they did the characters in his book. I hoped so. “The Buddha says that all suffering comes from clinging,” Matthiessen said. “I don’t want to cling. I’ve had a good life, you know. Lots of adventures. It’s had some dark parts, too, but mainly I’ve had a pretty good run of it, and I don’t want to cling too hard. I have no complaints.”

The characters in “In Paradise” cling too hard and are full of complaints, which is one reason that the book doesn’t feel like any kind of “final word.” The novel lacks the beautiful and affirming moments so much more present in Matthiessen’s nonfiction, moments more beautiful even than the dancing at Auschwitz, because they don’t come with the same complications. When Matthiessen was happy, as a writer and as a traveler, he always let us in on it; most often, he found that happiness in reverence of the natural world and in a hard-won, if fleeting, acceptance of his own uncertain place in it. “Lying back against these ancient rocks of Africa, I am content,” he writes in “The Tree Where Man Was Born.” “The great stillness in these landscapes that once made me restless seeps into me day by day, and with it the unreasonable feeling that I have found what I was searching for without ever having discovered what it was.”