The search for the missing pieces of the Golden Armour takes Cassie and Kieron to the hot and dry East Island where the water source is controlled by a tyrannical queen. The missing shield has to be found in order to bring water to the island.

Cassie, Keiron and their father are now on fog-bound East Island, a magical island where flying moonhorses and horrifying moonghosts delight and terrify the people in the shrouded city. Their search for the Golden Armour's Spurs is not going to be easy. Forced to seperate from their father, the twins are sent to an isolated school where the staff are stern and the rules frighteningly strict. Forbidden contact with the outside world, they feel imprisoned. But there they find a secret band of children and a legend in which they are to play a crucial part. Together, they pit themselves against enemies old and new in their fiercest fight yet, to secure the Spurs and save the island.

Cassie and Kieron are on the final part of their quest for the Golden Armour. Only the sword, hidden somewhere on flooded South Island, remains to be found. They enlist the help of the Merpeople, the stone giant and Merci the wild girl.