‘It is a déformation professionnelle: all spymasters go mad in the end,’ observes the hero of Robert Harris’s An Officer and a Spy, in what is clearly a warning from history. No dossier was ever as dodgy as that used in 1894 to convict Captain Alfred Dreyfus of treason; a barefaced collection of dud forensics and outright forgeries, it was never presented in open court for reasons of ‘national security’.

Dreyfus’s supposed deception was to pass military secrets, not even particularly important ones, to the Germans. His true crime was to be a wealthy Jew with financial interests in Germany during a period when paranoia about France’s old foe was at its peak and a xenophobic press operated unchecked.

Exiled to Devil’s Island, off the coast of French Guiana, the captain faced a punishment that was medieval in its cruelty. Deprived of human company, sometimes shackled to his bed, and confined behind a palisade that stopped him even seeing the