From Potters Field by Patricia Cornwell

Upon examining a dead woman found in snowbound Central Park, Kay Scarpetta immediately recognizes the grisly work of Temple Gault, a bold and brilliant killer from her past. Now she must hunt down a psychopath whose string of horrible murders is leading inexorably to his ultimate prey: Scarpetta herself. Even with the help of the FBI, Scarpetta knows the endgame is hers alone to play -- and it will be played on Gault's home turf, the subway tunnels beneath New York City.