A Necessary Evil  by Alex Kava

...Maggie O'Dell (after 2003's At the Stroke of Madness), the beautiful FBI profiler and recovering alcoholic suspects that more than one killer is involved in a spate of nationwide murders of Catholic priests. When Father Michael Keller, himself a serial killer, becomes a target, he tries to strike a bargain with Maggie in order to save his life. Their relationship will remind many of that between Clarice Starling and Hannibal Lecter...