Isabeau has immersed herself in the life of the Khan'cohbans but she still hopes to return to Eileanan from her self-imposed exile. First, though, she must undertake her journey of initiation to the Skull of the World, where the cruel and enigmatic Gods of White will reveal her destiny to her.
After successfully fulfilling her initiation quest, Isabeau returns to the Pride triumphantly and is given her initiation scar. She is now free to return to Lucescere and the Tower of Two Moons, where she plans to study to be a sorceress. Meanwhile, Iseult and Lachlan face new challenges to their rule. Although peace has been restored to the lands of Eileanan, the young Rìgh and Banrìgh have paid a high price for victory.
The Rìgh's army has marched upon Tìrsoilleir in an attempt to win back the throne for Elfrida NicHilde. But while Lachlan and Iseult are preoccupied with the invasion of Tìrsoilleir, Margrit NicFóghnan, the deposed Banprionnsa of Arran, kidnaps Lachlan's son Donncan.
It is Isabeau, though, who stands accused of treachery when little Donncan and Neil disappear, and yet no-one but she has the power to save the children from their fate at the hands of Margrit. This will be the truest test of Isabeau's Talent, a test which will threaten to destroy her and all she holds dear.
The Skull of the World is the fifth book in the series The Witches of Eileanan.