Chicago Assault (Hawker, #3)

Hawker returns to Chicago—where an old friend is about to die
 
When the police department told him to hold his fire, Hawker pulled the trigger anyway—and killed a dangerous terrorist. Since losing his badge, this hardnosed vigilante has been exiled from Chicago, the city he loves more than any other. He returns for the sake of one Saul Beckerman, a friend from the old neighborhood who has become one of the richest people in the city. Since Hawker began his nationwide war against organized crime, Beckerman has gotten into trouble with the wrong people, and even the nation’s most dangerous defender can’t save him now.
 
Hawker arrives at Beckerman’s penthouse just as his cocktail party is transforming into an orgy. Avoiding the writhing flesh of Chicago’s most powerful, Hawker takes his friend onto the balcony. He’s about to ask what’s troubling the man when the air is rent by a gunshot. Beckerman dead, Hawker sets out on a mission for bloody vengeance.
 
Chicago Assault is the 3rd book in the Hawker series, but you may enjoy reading the series in any order.