Here's the summary:
It is 1315. And darkness is falling . . .
Many generations ago the Wall was first built to hold back the sea. Northland, a country of fertile plains and ancient forests rescued from the ocean, has become a thriving civilisation based on trade, technology and tradition, centred on the ancient home of the first builders, Etxelur. The whole of Europe, spanned by the Northlanders' steam caravan lines, has been changed in ways that could never have been predicted.
But nothing can last forever, not even the Wall. The weather is changing, growing colder, and in the wake of the long winters come famine, destruction and terror. And as whole nations are forced out of their lands and head for warmer climes, it seems that even Northland may not be able to endure.
But there is one man, an elderly scholar, who believes he can calculate why the world is cooling, and perhaps even salvage some scraps of the great civilisation of Etxelur. As he embarks on his grand quest across the world, as nations struggle for survival and the fires of war burn in the gloom, only one thing is certain.
The Ice is coming.
Stephen Baxter's epic series of a changed world reaches its chilling conclusion as the medieval world fights for survival in the cold of a winter without end.