A mock French château in Minnetonka, a wealthy Minnesota suburb, seems an unlikely place for the headquarters of a business empire built on agriculture. Yet, from here, a group of little-known executives controls a business regarded as not only one of the most secretive but also one of the most powerful in the world.

Few people know much about Cargill. It has often tried to keep it that way. Even its chief executive admits that when he joined he could not tell his own father how much money it made. Yet Cargill's reputation for secrecy has masked a compelling story: how a business founded in 1865 has been able to grow into one of the 20 biggest in the US by revenue. More significantly, it has been able do so by remaining in private hands, relying chiefly on reinvesting its own cash.