Two worlds, Glandair and Iomard, draw near to each other every 700 years or so, in an occurrence known variously as the Settling or the Corruption. At these times, magical force grows stronger, bizarre phenomena occur, and those talented in various ways grow in their power and plot to advance themselves. In this treacherous time, three gifted young people: Cymel, Breith and Lyanz, each struggle both with growing up and with what these forces may mean to them or demand from them.
Its one of my quibbles with many fantasy & science fiction novels that the worlds created in their stories are very homogenous and simplified. In this, the most ambitious work by Clayton that Ive encountered (and her last Drums of Chaos was incomplete when she died in 1998), there are not one but two incredibly complicated worlds, filled with different cultures and factions. It takes some attention to keep it all straight but its a really interesting premise and setting. I like, too, how not too much time is spent explaining the alien aspects of each world the reader simply gets to experience it, and gleans information from context.
That said, this book is mostly scene-setting. Were introduced to many characters, and shown glimpses of their ruthless plots and ambitions we worry about our young protagonists, unwittingly caught up in forces beyond their control but not that much actually happens.