It is time for Simon Branthwaite to leave Sandarro, the city where he has lingered since reaching the fabled island of Rockall. Bidding a painful farewell to his new-found love, Princess Ilven, he sets out with Prince Avran to continue his quest for the lost realm of Lyonesse.

Travelling in secret - for their enemies are everywhere - Simon and Avran head north, into lands not marked on any map. Their path, through strange and wonderful terrain, is beset by savage beasts and hostile peoples, and many times they brush with death. Most ominous of all, they find themselves pursued by mysterious grey riders - men who bear the insignia of an evil empire of ancient times ...