Precious Blood — Jane Haddam

ASH WEDNESDAY, HOLY THURSDAY, DEADLY FRIDAY
Former FBI agent Gregor Demarkian is doing a friend a favor when he shows up in Colchester, New York. The Cardinal Archbishop has a problem: A young woman has been most mysteriously murdered, and one of his parish priests had the strongest of reasons for wanting her dead. But Father Andrew Walsh isn't the only one with a motive. It seems that quite a number of parishioners shared a damning past with the deceased.

SOME SUSPICIOUS SAINTS, A HERETICAL HOLY ROLLER, AND TWO CONSECRATED CORPSES...
THE EASTER HUNT IS ON FOR A CLEVER KILLER!
Something happened here twenty years ago. Something that's leading a desperate soul to break the deadliest commandment. And when the good Father himself keels over in the middle of High Mass, Gregor knows he needs a miracle.