With the Gathering Storm, the long dreaded cataclysm is about to descend on the world as the lost land of the Aoi returns to the earth from which it was cast forth into the aether millennia ago. And though Liath has at last found her way back from the land of the Aoi, she knows that disaster will soon follow her. Yet just how little time remains to avert humanity's destruction she discovers to her horror only when she learns that her brief stay in the bespelled land has actually kept her from her family and her allies for nearly four years.

In that time Sanglant has mobilized an army and journeyed to the land of the griffins, intent on forging an alliance to stand against the forces which are determined to rework the spell that originally exiled the Aoi and their lands from the world. Alain, caught up by Liath as she makes her way back to her own world and time, has been saved from the ancient cataclysm which began this terrible cycle, but he has been returned to the present bereft of all that matters to him. And though for a while he finds refuge in a monastery, he is soon condemned to a terrible fate. His only hope of rescue now lies with the Eika leader Stronghand, who has begun a campaign of conquest into the human lands. Through the link they share, Stronghand learns of Alain's plight and is determined to aid him, a decision reinforced when the Oldmothers order him to find Alain before it is too late. And even as these diverse forces struggle to avert the fast-approaching disaster, the mathematici, under the leadership of Anne and Hugh, strive to re-create the original spell which exiled the ancient Aoi, neither knowing nor caring that their magical workings could tear their world apart...