It is not hard, when confronting a subject such as Josef Mengele’s medical experiments on child twins in Auschwitz, to stir the emotions of the reader.

You don’t need to be a gifted writer to arouse pity, revulsion, abhorrence at descriptions of the defenceless and uncomprehending being scalded and infected, divested of their limbs; of the newborn baby seized from its mother and starved to death in a laboratory; of the Romanian boys whose arteries were sewn together in a bid to “create” conjoined twins. (Mengele was, among other things, medically incompetent and scientifically hare-brained.)

The skill, when addressing such material in fiction, lies in winning the attention of the reader in other ways, in creating credible characters, a fully realised world, or in doing interesting things with language and form: the stuff, in other words, of all good novels — except, given both the subject and its literary history, the stakes are rather higher, the potential for mawkishness, or cheapness, very great.

The problem with Affinity Konar’s Mischling is not that it’s not a particularly good novel, at times sentimental, glib and lacking in internal integrity: it’s that it’s a not particularly good novel about one of the darkest corners of the Holocaust .

At its centre are two twins, Stasha and Pearl, who arrive in Auschwitz as 12-year-olds in the autumn of 1944.

Immediately separated from their mother and grandfather, they are stationed in Mengele’s “Zoo”, where they are introduced to the Doctor’s gallery of damaged doubles: “In nearly every pair, one twin had a spine gone awry, a bad leg, a patched eye, a wound, a scar, a crutch.” They enter the camp thinking and speaking almost as one entity (“One of us snarled. It might have been Pearl. It was probably me”). This singularity will soon be ripped apart.

There is a fabular quality to both the narrative and prose, dreamy language used to describe a nightmare. It is an interesting approach but the result is too often hollow and evasive, as opposed to anything appropriately disturbing.

To divide responsibility, the twins decide to “share out” emotion and time: “Stasha would take the funny, the future, the bad. [Pearl] would take the sad, the past the good.” Mengele, too, divides responsibilities: Pearl is infected with a pox; Stasha is made partially deaf when boiling water is poured into her ear. It leaves her with a permanent echo. “This was good when someone said something pleasant. It was terrible when someone barked a nasty order.”

The cutesiness of the above sentence, its straining for effect, should give some indication of what we’re dealing with. Elsewhere, “heartbeats” are euphemistically “extracted” from bodies, while working for Mengele is like “stringing a harp for someone who played his harp with a knife.”

Quite a lot happens: the children devise games (these sections are largely vivid and well-researched) and endure appalling horrors; they develop crushes and enmities, plot their escapes; then Pearl disappears. Later, the camp is liberated and Stasha’s search for her lost double begins. There are various resolutions, daubed with schmaltz.

Clever leitmotifs are capably woven in: ideas about individuality and classification, imagination and transcendence. Konar can write well and will write well again. But Mischling too easily betrays the workings of its research and its thematic preoccupations. Worst of all, for a book about the Holocaust, it just doesn’t ring true

Toby Lichtig is the fiction editor of the TLS