Josef Mengele, the Nazi “Angel of Death” who presided over medical experiments at Auschwitz, was never captured. He drowned on a beach in Brazil at age 67 — a swifter and less agonizing death than he afforded the 3,000 twins who were the subjects of his gruesome mutilations and surgeries. Some 160 survived.

Affinity Konar’s unflinching second novel, “Mischling,” imagines the children’s lives at Auschwitz and the process by which they managed to carry on after the war. The novel acknowledges its debt to the seminal nonfiction book on this subject, “Children of the Flames,” especially the story of Romanian twins Eva and Miriam Mozes. The women founded a support group for other survivors of “the Zoo,” as Mengele’s compound in a former horse stable was nicknamed.

Pearl and Stasha, the heroines of Konar’s novel, are identical 12-year-old twins, with blond hair that Mengele believes proves them “mischling,” or only part Jewish, under the Aryan racial laws. Many of the descriptions of the camp, from the arrival of the cattle cars to the crematoria, will not be news to anyone who has been to the Holocaust Museum, seen “Schindler’s List” or read any of the great memoirs on the subject, such as Primo Levi’s “Survival in Auschwitz.” But Konar draws us quickly from that familiar landscape to the bizarre world of the Zoo, focusing on the twins’ special bond.

In alternating chapters, the girls chronicle their diametrically opposed mechanisms for coping with the horrors they experience. The more extroverted Stasha becomes intent on revenge, but also on keeping her humanity. “Such darkness should make life impossible, I know,” she asserts, as she forms alliances with others in the camp. “But my other part? It was wild hope. And no one could extract or cut or drain it from me. No one could burn it from my flesh or puncture it with a needle.” As Stasha becomes bolder, Pearl withdraws, keeping meticulous notes of the other children’s diseases and deaths — a form of bearing witness.

Konar unveils Mengele’s atrocities gradually and only in glimpses. Stasha sees the thousands of human eyes pinned to the wall in his office, part of his pet project to change eye color to the preferred Aryan blue. It gets much worse before it gets better as the twins are separated, and Pearl is subjected to ever more severe torment, with Stasha as control group for sympathetic suffering.

The novel’s second half takes place after the camp’s liberation. Konar constructs a sinuous plot from the chaos of the postwar landscape. The faster pace frees her from the burden of having the children quite so lyrically narrate their own suffering.

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The morality of fictionalizing the Holocaust has been a subject of scholarly discussion since philosopher Theodor Adorno famously declared, “To write poetry after Auschwitz is barbaric.” Do the scaffolding of plot and invention, the linguistic embroidery, deny the actual victims their more authentic voices? Conversely, might fiction have “the power to take the narrative to places that survivor testimony cannot?” as Anna Richardson asks in her essay “The Ethical Limitations of Holocaust Literary Representation.”

Certainly Konar is sensitive about the dangers of seeming sensationalistic, or voyeuristic, by lingering too long in the chamber of horrors. Miri, a Jewish doctor forced to assist Mengele, agonizes after liberation: “These are only some of the brutalities I can speak of. They are too innumerable and varied, so grotesque — I do not have the words.”

Yet the project of “Mischling” is precisely to find the words. Readers’ reactions to the novel will largely depend on how they feel about touring the Zoo with Konar as guide, rather than learning about this cruelty in a more documentary format — or from an actual survivor, like Nobel Prize winner Imre Kertesz, whose novel “Fatelessness” draws from his own experiences at Buchenwald. I would not want to argue that only survivors are entitled to approach this subject matter, although obviously they have an advantage. Jim Shepard’s novel “The Book of Aron,” grounded in massive research on the Warsaw Ghetto, reaches astonishing heights of empathy and insight.

Of course, fact and fiction needn’t be enemies. “Mischling” may send some readers unfamiliar with this material back to “Children of the Flames,” whose authors have endorsed this novel. It is certainly miraculous, and moving, that any of these victims survived, and Konar is wise to keep her focus not on the incomprehensibly sadistic Mengele in his shiny black boots, but on the children themselves.