Girona, Spain, 1353. Isaac is called in on the cases of three young men who die suddenly of a strange illness signaled by sleepwalking, delusions, and strange mutterings. The physician suspects poisoning, but others believe witchcraft may be the true cause. Soon a new disease is spreading through the city -- one just as cruel and insidious as the plague. For now that there are rumors of a supposed witch in their midst, any woman might be accused by the irate townspeople. Now Isaac must use every skill in his power to discover the murderer, cure Girona of its deadly hysteria, and expose the charlatan who caused it.