True Believers — Jane Haddam

There's hell to pay in Philadelphia when Marty Kelly commits suicide over his wife's body in the sacristy of St. Anselm's Church. Everyone assumes that Bernadette Kelly, a diabetic, died of natural causes--until the autopsy reveals death by arsenic. But one of the nuns a St. Anselm's, certain of Marty innocence, recruits retired director of the FBI's Behavioral Science Unit Gregor Demarkian to investigate for the new Cardinal Archbishop. His Eminence, dispatched to Philadelphia to clean up a scandal, expects Demarkian to act with discretion. But when a third death by arsenic is revealed in the neighboring Episcopal Church, not even God's grace can help the priest who becomes a prime suspect--and the murderer's next victim. Moving among three combustible parishes--Catholic, Episcopalian, and rabble-rousing fundmentalist--Demarkian must negotiate his way through holy hell to find the diabolically clever killer. Only then may God's will--and a homicidal reign of terror--be done...