Roland Barthes, one of the twentieth-century’s towering literary figures, is knocked down in a Paris street by a laundry van. It’s February 1980 and he has just come from lunch with Francois Mitterrand, who is locked in a battle for the Presidency. Barthes dies soon afterwards. History tells us it was an accident. But what if it were an assassination? What if Barthes was carrying a document of unbelievable, global importance? That document was the key to the seventh function of language – an..