The book follows the life of Jemmy Bloocher, (who changes his name several times) as he travels the planet called Destiny, a colony founded over 200 years earlier. The "Road" is a long trail laid down by the founders. Only the Caravans travel the full length of the road as they bring (or sell) "speckles" to settlers who, without them, would suffer severe potassium deficiency leading to brain damage. The Caravans control who gets speckles and therefore effectively control the whole world. Jemmy sets off to find answers to questions the Caravan Merchants won't give him. In the process, we get a good look at the world and also at it's economy. Larry Niven's world-building skills are phenomenal, and this book is a good example of just that. There is room to develop the native alien sapients ("Otterfolk") further, perhaps in a sequel.

This is "hard" science fiction in that the medical (potassium) and economic (hydraulic empire, resource domination) foundations of the book are soundly researched. But it is relatively "soft" for "hard" fiction, as there is very little exposition or explanation of the science involved.