SFPD Detectives Terry English and Hildy Mulligan are quickly thrust into the middle of a brutal onslaught as two students open fire on a school bus in the middle of the city. San Francisco's finest must work quickly in order to put an end to one of the deadliest shootings in recent history, as one gunman is captured, and the other escapes.

As the city reels from the school bus tragedy, newly appointed D.A. Mario Siletti promises justice for the victims. Terry receives new evidence about the recent death of a cop, leading him to believe it may have been of a more insidious design. Meanwhile, the body of a young Chinese gang member found in an urban grow house, leads Hildy into the dangerous world of drugs and gang politics.