Harry Turtledove 
Bridge of the Separator [EPUB ebook] 

Rhavas is a good, holy, and pious man, as befits a member of the clergy. He is also the cousin of the Avtokrator, ruler of the Empire. Hoping someday to become ecumenical patriarch of Videssos, he was reluctantly willing to bide his time in one of the smaller cities on the outskirts of the Empire.Then civil war broke out, and the Avtokrator had to pull back the troops guarding the borders as he struggled for control of the Empire. Rhavas had to flee for his life as the fierce Khamorth nomads took advantage of the chaos and sacked the city he had come to love. He only survived because he accidentally discovered that he had an unsuspected power: Men often cursed each other — but Rhavas’s curse had the power to kill!Rhavas had always followed Phos, the god of light and goodness, Videssos’ own god, just as he had always despised Phos’ evil rival Skotos. Those who fall off the Bridge of the Separator during judgment in the afterlife are doomed to dwell in Skotos’ ice and darkness forevermore. But Rhavas has reverenced logic as well as goodness, and knows the power to kill with a curse cannot be an attribute of Phos. As evil swallows up the world, Rhavas, ever the logician, decided that Skotos is actually the more powerful god, and becomes determind to change the official religion of Videssos. But in the end, it is he who will be changed, and neither the world nor he will ever be the same again…