A black woman is stopped by police and taken into custody. The next morning, she is found dead in a cell, murdered. The police have no record of her arrest and the surveillance feed has gaps in it, covering her entrance and that of the killer.

The nation is again outraged as charges of brutality are leveled on law enforcement. The national media, the Black Lives Matter movement and others descend on the city, putting Detroit in society's crosshairs.

The case is assigned Police Internal Affairs but Danny Cavanaugh has a compelling reason to work on the case in secret: the murdered woman was his beautiful and provocative sister-in-law.

Danny takes up an unauthorized investigation, always one step behind the ruthless killer who knows just how to cover his tracks, getting rid of precious evidence and witnesses.

Danny plunges into the case, tramping through Detroit as winter is coming and the city, fresh out of the largest municipal bankruptcy in history, has everyone, rich and poor, criminal and legit, scrambling to get ahead, or "On the Grind" as they say on the street.

With time running against him and enemies all around, Danny is on familiar turf, but he has never faced a nemesis so clever, nor has he ever had so much to lose. As he closes in, the case takes a turn that plunges him into the abyss of the criminal mind, where he finds a motive more evil than murder.