Last July a German doctoral student named Matthias Weßel made a remarkable discovery. He was examining the papers of the late Swiss publisher Emil Oprecht for a dissertation on Arthur Koestler’s transition from writing in German to writing in English at the end of the 1930s. Oprecht was a left-wing fellow traveler who had founded his famous publishing house Europa Verlag in Zurich in 1933, and was well known for his anti-Nazi views and support for writers in exile, including Thomas Mann, Stefan Zweig, Ignazio Silone—and the young Arthur Koestler. Weßel told me that at the time, “I was looking for letters and royalty reports, because I wanted to know how many copies were printed of the first German edition of Koestler’s Spanish Testament.” He failed to find the answer to his question, but while looking over the Europa holdings in the Zurich Central Library he came across a cryptic entry: “Koestler, Arthur. Rubaschow: Roman. Typoskript, März 1940, 326 pages.”

This was extremely odd. Weßel knew of no such novel (Roman) in Koestler’s German writings, but the name Rubaschow rang a bell. Rubaschow (in English, Rubashov) is the hero of Koestler’s finest novel, Darkness at Noon. Weßel hardly dared think about what he had found, suspecting a sequel or perhaps a false entry, for it was well known that the original text of the novel—the last one Koestler wrote in German before he switched to English—was lost during his flight from France at the start of World War II. That was seventy-five years ago and it has never been seen since. With trepidation, Weßel ordered a scan, which showed a typed carbon copy, with corrections in Koestler’s handwriting. The date on the title page, March 1940, was the date on which Koestler is known to have finished the novel. There was no doubt. Weßel had stumbled across a copy of the German manuscript of Koestler’s masterpiece.

The implications of Weßel’s discovery are considerable, for Darkness at Noon is that rare specimen, a book known to the world only in translation. This peculiar distinction has been little discussed in the vast critical literature about Koestler and his famous novel. In my lengthy 2009 biography of Koestler I barely touch on it, yet the phenomenon is all the more extraordinary when one considers that the novel has been translated into over thirty other languages, every one of them based on the English edition, meaning that they are not just translations, but translations of a translation. This includes the German version, which Koestler himself translated back into German in 1944.

It is not certain that the Zurich typescript is the absolutely final version of Koestler’s novel, but it’s undoubtedly very close. Weßel has compared it with Koestler’s back-translation, and while the plot and characters are the same, he has found a…