A good work of detective fiction will leave enough things to doubt, ponder over and marvel at even after the crime is solved. A real-life historical thriller -- a world of abstract symbols and broken seals, decayed teeth and unknown languages – is even more capable of retaining an essential mystery in its womb. The story of the Harappan civilisation, true to type, is one of alternating light and darkness. In the fourth and third millennia BC, the subtropical sun shone on a culture of astonishing order and symmetry. Then a long night descended. The curtain parted only a century ago: the spectacle hazy to begin with, but the mist lifting slowly as a sheer richness of detail presented itself…. Then, because this is a world where ‘interpretations’ can be more resilient than ‘facts’, the fog of war descended. At long last, a cold, sober light is cutting through the opaque air to reveal a landscape of hard truths. Many of these had long been sussed out through archaeology and linguistics, but genetics has now lent a blade-edge sharpness to our mental picture.