Phantom in the Night by Sherrilyn Kenyon

After losing her mother to a vigilante killer, Terri Mitchell has dedicated her life to justice. Working covertly as a new agent for the Bureau of American Defence agency, she's consulting with the New Orleans Police Department to bust an organised crime ring suspected of funding terrorism. But when rumours surface of a phantom ghost terrorising and killing the very people she's investigating, she's suspicious.
Nathan Drake has spent his life protecting his family, the only thing that matters to him...until the most feared drug lord in the southeast takes everything Nathan holds dear. Now he's a man on a mission with nothing to lose. He figures he only needs to stay alive long enough to protect the innocent lives the killers are out to destroy.
As the two of them seek a similar goal by different means, Terri and Nathan are drawn deep into an evil underbelly that cuts through all levels of society. Now two people who have no reason to trust must trust in each other or die. And if they die, a deadly attack will be unleashed on thousands of innocent people.

This book is part of the "B.A.D. Agency" series.
Here are some other books from this series: