Southern Fire — Juliet E. McKenna

Their coming had not been written in the stars, and no augury had foretold the terror they would bring. The first sign was the golden lights of the beacons, a clear message from every southern isle that a calamity had befallen them.
Daish Kheda, warlord, reader of portents, giver of laws, healer and protector of all his many-islanded realm encompasses, must act quickly and decisively to avert disaster.
But the people of the Aldabreshin Archipelago not only fear magic, they've abjured it. So what defense can Kheda offer against the threat of a dark magic that threatens to overrun every island of his domain?
A new tale from the writer who has already gathered many fans with the five volumes of her Tales of Einarinn, Southern Fire is an engrossing epic of magic, intrigue, culture, and politics, in a fantasy setting as colorful as the south seas, as bracing as the ocean wind, and as alluring as the hint of spices in the air of an exotic port.