Crystal Vision by larry Rodness

Scotland, 1342.
The Great Plague ravages the countryside. In its wake the body of a beautiful young noble woman, Ariella, is laid to rest on a funeral pyre. Her fiancé, Darcy McKee, begs a sorcerer, Armand, to use his magic to bring the young woman back in exchange for his own. Armand summons a demon with the power to do just that.

Fast Forward to:
America, 2008. Fourteen-year-old Jeremy McKee is obsessed with a fantasy workshop downtown and the beautiful young woman who owns it. One afternoon, Jeremy is approached on the street by a vagrant who offers him a small crystal which produces visions of a young woman resurrected from death hundreds of years ago.
Slowly, the truth begins to reveal itself. The young woman in the vision is Ariella and the vagrant is a sorcerer, Armand, who was responsible for bringing her back to life. He explains to Jeremy that his ancestor, D’Arcy McKee, offered his soul for the life of his betrothed but reneged at the last minute. Now the demon has returned for payment. And he’s prepared to unleash the Plague if he doesn’t get what he wants.