Four thousand years ago, someone in Mohenjo-Daro carved a tiny stone seal. On it: a unicorn with muscles so finely rendered you can count the tendons, and above it, a string of mysterious signs that no one has been able to read since the city fell silent. That seal survived earthquakes, floods, and the full weight of four millennia. It looks like it was made yesterday morning.

For a century, scholars tried to crack the Indus script the way you crack a code—by finding the language hidden inside. They all failed. Every last one. Not because they weren't brilliant, but because they were asking the wrong question. The Indus seals were never letters in a language. They were something far more interesting: the world's first information system. A structured code that identified people, goods, and transactions across an entire civilization—without a single word of grammar.

This is the story of how that discovery was made. It involves seven groups of researchers spread across a hundred years and five continents. A Finnish professor who spent half a century chasing fish-shaped rebuses. A software engineer from Kolkata who saw tax receipts where everyone else saw prayers. Three scholars who declared the whole thing wasn't writing at all—and got death threats for their trouble. A Tamil Nadu government that offered a million dollars to anyone who could solve the riddle. An information theorist who studies cat behavior and compression algorithms. A systems theorist in Toronto. And an artificial intelligence that, in one three-hour conversation, ran the statistics that changed everything.