Sorcery rising - Jude Fisher

From the barren isles of the North come the Eyrans. Hardy seafaring folk. From the South come their old enemies, the Istrians. Slave-owners, who drove the Eyrans from their lands. And from all over Elda come the nomadic peoples - the Footloose - purveyors of charms and (until now) harmless potions. But whence comes the sorcery that disrupts the annual Allfair at which they all gather?
Katla Aransen and her family have sailed to the fair to trade their goods. The Vingo clan have travelled from Istria to purchase a bride for their appalling eldest son. Tycho Issian has come to sell his daughter to the highest bidder. King Ravn Asharson, Stallion of the North, seeks a political alliance; while others seek his downfall.
For centuries, Elda has been bereft of magic; but this year something has changed. A mysterious force is abroad once more, and it will change the world forever...