Russ Pennington 
The Last Good Christian 

The year is 1968

In a gritty New England city, two days before Christmas, a priest is discovered hung up on rocks in a river, murdered. The killer is never found and the case goes cold.

Twenty-eight years later, the perpetrator resurfaces

Obsessed by the Medieval Inquisition’s assault on Cathar heretics, a religious fanatic becomes an avenging angel by subjecting the Dominican brotherhood at a Rhode Island college to the same penances and punishments that their 13th and 14th century counterparts inflicted on the Lanquedoc’s unbelievers.

An unsolved case is re-openned

Police detective Georgette Duby, saddled with serious domestic baggage, stalks the murderer. Trip Allen, an amateur historian holding the key to the perp’s identity, aids her only to have the tables turned on them.