“Arbeit Macht Frei”: the words over the gate to the entrance to Auschwitz translate as “work makes you free”, though in fact the work done there mostly either killed you in itself, or preceded your extermination.

There were some survivors, of course, and for one of them, Primo Levi, it would be words that would make him free. A year after he was liberated from Auschwitz by the arrival of Russian troops in January 1945, he started to write a book about his experiences, and the result was first published in his native Italy in 1947 as Se questo e un uomo.

It would be another 12 years before it was translated into English and subsequently first published in Britain and America as If This Was a Man. It still stands as a hauntingly personal testament to one man’s survival against the odds. Now the actor Antony Sher has adapted it for the stage as Primo. The resulting one-man play, which Sher himself performs, is a quietly overwhelming, intensely compressed re-telling of a harrowing true story that makes for utterly gripping theatre.

Born in Turin, Italy, and trained as a chemist, the 24-year-old Jewish Levi was arrested in December 1943, and transported to Auschwitz in February 1944. There, he would become 174517 – a new name tattooed to his arm that he would see whenever he looked for the time on a watch that was no longer there, but as he might have done when he was still free.

Beyond these biographical details, the brutal everyday outrages of what happens inside the camp is full of the kind of detail that’s both heart-stopping and gut-wrenching, all the more powerful for being told with such calm authority and quiet dignity. How do we ever come to grips with trying to fathom the unfathomable?

This piece doesn’t make claims to help us do so, but it’s shot through with insight and humanity in the face of a terrible inhumanity. Arriving at Auschwitz and deprived of water for four days, Primo remarks, “Hunger exhausts, but thirst enrages.” Stripped and entirely shaved, even of their body hair, he comments that the inmates are “as naked as worms.” Average life expectancy in the camp is eight weeks – survival depends on learning to obey orders in a language you don’t understand, and having a pair of shoes that fits.

As these and other gruelling documentary details emerge, Sher – moving around a stage enclosed by bare walls designed by Hildegard Bechtler under the unobtrusively sharp direction of Richard Wilson - completely inhabits this man. One of our most chameleon-like actors, Sher gets under his skin, in a play that will get right under yours.

- Mark Shenton