Something is happening in the small village of Helsop. A trader has gone missing. While Esme waits to hear more from her friend Dag the Scout, her twin Shalin and mother Serafina arrive from Henge with an invitation.
Helsop is invited to a celebration in Henge. But there appears to be an ulterior motive behind the invitation – a plan to devise a new strategy to loosen the Great Khan's hold over the trade routes of the world.

In this thirteenth year of the Royal Twins Chronicle, they will find themselves on another journey to Timbitu, this time with a caravan of camels trekking over the Atlas Mountains of Tangier and across the Great Sahara desert, buying salt to exchange for gold along the way.
Will Serafina find the volatile secret she seeks?
Will the twins discover the real reason their father has allowed them to go on this voyage?
The answers are here in Book Four: a Map of the World.