The Fifth Angel (Green, Tim)

Jack Ruskin is uniquely qualified to commit a series of perfect murders. A former prosecutor, and now the respected partner of a prestigious law firm, he has the means and the knowledge to kill without leaving a trace of evidence behind.
His targets are criminals themselves, sexual predators beyond reform. He has no connection to them; he simply finds their names in public records. But Jack knows firsthand the devastation these depraved monsters leave in their wake - his own fifteen-year-old daughter was herself a victim. And he's determined to save others from the same excruciating pain.
A thousand miles away, FBI agent Amanda Lee has carefully balanced motherhood with her meteoric career as one of the agency's brightest and bravest experts in her field. Then a botched investigation rocks Amanda's life as well as her career, and she is assigned to a case some people don't want to see solved. Following the trail of the man who is stalking sex offenders across the country, Amanda is unaware that her past is catching up with her and that she - and her children - are in the gravest danger.
As Jack carefully, methodically, and brutally exacts his own brand of justice, Amanda closes the gap between them. But in an astounding twist of fate, their lives are about to fall into each other's hands. Before the hunt is over, they will have to choose together: between deliverance and destruction, and between the ultimate right and wrong.