Brian Aldiss 
Helliconia Winter 

The third and final book in the epic Helliconia trilogy. The centuries-long winter of the Great Year on Helliconia is upon us, and the Oligarch is taking harsh measures to ensure the survival of the people of the bleak Northern continent of Sibornal. Behind the battle with which the novel opens lies an act of unparalleled treachery. But the plague is coming on the wings of winter and the Oligarch’s will is set against it — and against the phagors, humanity’s ancient enemies, who carry the plague with them.