The Chronicle of Sword and Sand, book 2: The Bones of the Old Ones
Howard Andrew Jones2012

As a snowfall blankets 8th century Mosul, a Persian noblewoman arrives at the home of the scholar Dabir and his friend the swordsman Captain Asim. Najya has escaped from a dangerous cabal that has ensorcelled her to track down ancient magical tools of tremendous power, the bones of the old ones.

To stop the cabal and save Najya, Dabir and Asim venture into the worst winter in human memory, hunted by a shape-changing assassin. The stalwart Asim is drawn irresistibly toward the beautiful Persian even as Dabir realizes she may be far more dangerous a threat than anyone who pursues them, for her enchantment worsens with the winter. As their opposition grows, Dabir and Asim have no choice but to ally with their deadliest enemy, the treacherous Greek necromancer, Lydia. But even if they can trust one another long enough to escape their foes, it may be too late for Najya, whose soul is bound up with a vengeful spirit intent on sheathing the world in ice for a thousand years...