Winemaker of the North by J.T. Williams

Sviska is an assassin sent undercover as a winemaker to a desolate city in the mountains. He leaves his world devoid of magic and finds that this city is actually a refuge for the last elves, dwarves, and magic folks of the land. A curse destroyed the many cultures of magic and the city has shielded them from its effects. Now the shield fails and the city relies on a medicinal wine brewed by the elves but the last winemaker was murdered. Through uncovering a plot within the city itself, Sviska fights a necromancer and his summoned demon, agents of his Order sent to assure his work is completed, and his own conscious over his duty. Those that sent him wish for him to poison the wine and when he does not, they move to strike the city with the armies of men. Sviska fights and escapes with a secret and his own tie to his lost ancestery. He is to return magic and he is the last hope.