One night in March 1944, a young member of the French Resistance, codenamed “Greco”, landed in occupied France from England. His main mission was to connect Parisian résistants with London. He was betrayed to the Gestapo, who waterboarded him and sent him to Buchenwald. Just before he could be hanged, he swapped identities with a dead French prisoner.

And now, aged 93, Stéphane Hessel tops France’s bestseller lists. His 12-page left-wing pamphlet Indignez-vous! (“Be Indignant!”) has sold 500,000 copies since October. His tiny publisher, with just two full-time employees, is overwhelmed.

The most obvious lesson is that people should write 12-page books. The traditional 250-page model probably stopped being appropriate with the disappearance of the attention span. But Hessel’s sales also reveal something about France, and about the left everywhere.