Early one morning at St. Anselm's church in Philadelphia, a parishioner sneaks the body of his dead wife into the sacristy and commits suicide. His wife, a severe diabetic, is assumed to have died of natural causes - until the coroner discovers arsenic poisoning. The police are sure her husband was responsible, but one of the nuns at St. Anselm's doesn't and asks Gregor Demarkian, retired head of the FBI's Behavioral Science Unit, to investigate. With tensions mounting among the city's religious groups, Demarkian's lover Bennis undergoing a crisis of her own, and the denizens of Demarkian's Armenian-American neighborhood - Cavanaugh Street - involved in various uproars of their own, Demarkian is facing the most difficult case of his career.