an alternate cover edition can be found here

As far as she can tell, Nell Harris is either going insane or she is in love. Nell thought she had been summoned to Prague to work on an inscription in a rare fourteenth-century breastplate. Instead, she is immersed in the world of the Moravian Dark Ones (think vampires) when she is swept up in the search for a boy held captive by the demon lord Asmodeus. Although Nell would like nothing better than to use her powers as a "Charmer" to help find the missing boy, the last time she dabbled in magic the consequences were dire. Then Nell meets Adrian Tomas. Bound to serve Asmodeus and forced to betray his fellow Dark Ones, Adrian desperately needs Nell to charm away his curse. One look into Adrian's haunted eyes, and Nell discovers she will do just about anything to save the soul of her new beloved.