“Everyone who is born holds dual citizenship,” declared Susan Sontag in the opening pages of “Illness as Metaphor” (1977), “in the kingdom of the well and in the kingdom of the sick.” At the time she wrote these words, the author had just recovered from a nearly fatal struggle with breast cancer. She was, alas, destined to return to the kingdom of the sick not once but twice. In the late 1990s she survived a uterine sarcoma. And in March 2004, she was diagnosed with MDS, or myelodysplastic syndrome — a form of cancer that eventually mutates into leukemia, destroying the body’s ability to manufacture mature blood cells.

A diagnosis of MDS is essentially a death sentence. But Sontag, then 71, had no intention of relinquishing her grip on life. She opted for a bone marrow transplant, fully aware that this horrendously painful procedure stood little chance of beating back her illness, and refused to surrender all hope until the very end, which came on December 28 of that same year.

Had there been any point to her suffering of the previous nine months? Should her friends and family have discouraged what her son David Rieff calls her “revolt against death”? These are the questions at the heart of Mr. Rieff’s “Swimming in a Sea of Death” (Simon & Schuster, 196 pages, $21), and it should be said at the outset that they can’t really be answered. They are metaphysical riddles, attempts to slap a price tag on such intangibles as pain and hope. They are also, when posed by a grieving son, instruments of self-recrimination, which the composition of this brief memoir seems to have alleviated very little.

Indeed, three years after his mother’s death, Mr. Rieff is still flogging himself for saying the wrong thing, or for sometimes saying nothing at all. Recalling one such stunned silence, he writes: “Perhaps some people transcend themselves when a loved one becomes ill, become demonstrative where before they were inhibited or withholding, and cheerful where before they were morose. But even if that’s the case, I was not able to become one of them. Instead, I said nothing. My mind was a doleful blank.”

In situations such as these, the prospect of personal transcendence is largely a myth. Mr. Rieff, whose relationship with his famous mother remained on the rocky side, would operate within his own, very human limitations. So too would Sontag, whose confidence in her own survival amounted to a kind of personal religion. She simply would not accept the fact of her impending death. Back and forth Mr. Rieff goes, unable to decide whether her final struggle was admirable — a testament to her “childlike sense of wonder” — or a self-destructive folly.

The answer may be both. But that’s not satisfactory for the author, who keeps dredging for something better, even as he admits that language is inadequate to the task. On the very day of her diagnosis, Mr. Rieff recalls, this weakness was cruelly exposed: “What my mother and I shared were words and yet now they felt all but valueless — like Confederate dollars or Soviet roubles.”

That words fail us in the face of death is a given. That they sometimes fail us before a blank sheet of paper is another matter entirely. As he tells us, Mr. Rieff made a conscious decision to take no notes during his mother’s ordeal. “Perhaps no writer can escape the sliver of ice in the heart that is one of the professional deformations of their craft,” he concedes, “but to the extent I could, I wanted no ‘writerly’ distance to separate or protect me emotionally from the reality of what was going on.”

As a survival mechanism, and an attempt to short-circuit any retreat into the inner sanctum of art, this is perfectly okay. Yet Mr. Rieff’s discomfort with the details — surely his stock-in-trade in his previous studies of Cuba, Miami, or Bosnia — gives “Swimming in a Sea of Death” a muffled and meandering texture. Unlike his mother, Mr. Rieff is a born reporter, drawn to stories instead of the great abstractions. But since organizing his mother’s extinction into a shapely narrative strikes him as a sort of sacrilege, there is no story. There are only those same unanswerable questions, surfacing over and over in this increasingly disheveled, redundant book.

It is only when Mr. Rieff surrenders to specificity that his memoir truly comes alive. His account of Sontag’s final hours is vivid, as are the few paragraphs he devotes to her burial in Paris. “The journey began over the Atlantic,” he writes, “me in my window seat, the tranquilizers having zero effect, she in the hold. And it ended in the Volvo hearse that moved smoothly from the funeral home at the edge of the city to Montparnasse, along the boulevards that she had known so well and loved so ardently…. I took my mother on one last, sweeping ride through Paris, and then I buried her.” A painful journey, and no doubt painful to recall. But to quote from Robert Lowell’s own valedictory verse, in which the poet debates the very value of the “poor passing facts” before coming down in their favor: Why not say what happened?

Mr. Marcus is a critic, translator, and the author of “Amazonia: Five Years at the Epicenter of the Dot-Com Juggernaut.”