The Way Back by Gavriel Savit
For the Jews of Eastern Europe, demons are everywhere: dancing on the rooftops in the darkness of midnight, congregating in the trees, harrowing the dead, even reaching out to try and steal away the living.
But the demons have a land of their own: a Far Country peopled with the souls of the transient dead, governed by demonic dukes, barons, and earls. When the Angel of Death comes strolling through the little shtetl of Tupik one night, two young people will be sent spinning off on a journey through the Far Country. There they will make pacts with ancient demons, declare war on Death himself, and maybe– just maybe–find a way to make it back alive.