The Stone of Darkness by Resa Nelson
In Book 3 of the Dragonslayer series, Astrid accepts her duty and follows the winter route--until she's bitten by a dragon.
Everyone knows dragon bites are poisonous and deadly, so she reluctantly accepts her impending death. In a twist of fate, she survives. Desperate for an explanation, Astrid believes she has somehow been protected by the black stone she keeps with her at all times, a stone that emerged from the sole of her foot a year ago.
Determined to find out what the stone is and what kind of powers it possesses, Astrid begins a journey that leads her to alchemists and an army of men under the rule of the powerful warrior, Mandulane, the acting lord of the Krystr army. Mandulane's mission is to spread the word of the new god Krystr, which preaches the evil intent of women and the danger they pose to all men, who are entitled to dominate the world. Rumors about this new god and army have spread, but Astrid is the first Northlander to encounter them. Soon, she stumbles upon a secret of a far-reaching and mind-numbing plot that will impact the entire world.
Astrid must find a way to spread the news of this threat and protect her people and everyone else at risk. She's convinced the answer lies inside the Stone of Darkness, and she must find a way to understand the stone and the powers she's convinced it must hold before it's too late.