The Pale Horse by Christie, Agatha

Wickedness...such wickedness...."
The dying woman turned to Father Gorman with agony in her eyes. "Stopped....It must be stopped....You will...."

The priest spoke with reassuring authority. "I will do what is necessary. You can trust me."

Father Gorman tucked the list of names she had given him into his shoe. It was a meaningless list; the names wer of people who had nothing in common.

On his way home, Father Gorman was murdered. But the police found the list and when Mark Easterbrook came to inquire into the circumstances of the people listed, he began to discover a connection between them, and an ominous pattern....

Every name of that list was either already dead or, he suspected, marked for murder.