San Francisco Police Department Detectives Terry English and Hildy Mulligan are quickly thrust into the middle of a brutal onslaught. San Francisco's finest must work quickly to put an end to the threat.

Tensions mount as the manhunt proves to be more difficult than expected. Terry is promoted to acting lieutenant, which he soon discovers comes with responsibilities more taxing than he anticipated.

As the city reels, newly appointed D.A. Mario Siletti promises justice. 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.

Raffi fears Hildy's continued investigation of the grow house murder will blowback on a case of her own.

Terry and Hildy find themselves investigating people within their own department. Jamie digs into Dustin's past in an effort to better understand his actions. Meanwhile, Suger searches for answers as someone close to him disappears, then makes a shocking discovery.

Terry and Hildy head to Mexico when truths emerge about Navarro. Meanwhile, a fuming Suger prepares for war, and unforeseen developments mark Raffi's investigation into Suger.

Junior reveals new details which may finally give Hildy and Terry the upper hand in their investigation, while the Trial of Dustin Maker begins with opening statements. Meanwhile, an unlikely source provides Suger with startling new information regarding his sister.

Terry and Hildy's investigation is dealt a lethal setback; Raffi's loyalty is questioned; Suger contemplates the future of Potrero; the stress of the trial takes a toll on Jamie.

While Jamie deals with the fallout from her tirade, witnesses begin to take the stand in the case against Dustin; Hildy makes a vow when her family is threatened.

Terry and Hildy take a high-ranking officer into custody; Suger faces a new threat to Potrero; Molk uncovers unsettling information about a potential prostitution ring.

Terry and Hildy race to close in on a murder suspect; Fatty B lobbies to take Potrero in a new direction; a verdict is reached in Dustin's trial.

Homicide Inspectors Terry English and Hildy Mulligan investigate when an all-star quarterback is murdered in the middle of a crowded club in front of his pop star girlfriend. D.A. Mario Siletti and his wife are involved in a tragic car accident that could end his career and his marriage. And an untimely diagnosis threatens Hildy's future.

As the hunt continues for the prime suspect in the Normandy Parker case, an anonymous tip forces Terry into an officer-involved shooting that sets off public uproar. A desperate Siletti reluctantly hires DUI defense attorney Alfred Arkin but withholds essential trial information. Hildy gets good news for her future, and she and Terry cross a line together.

Disturbing new information about Normandy parker lengthens the list of suspects in his murder. Siletti, fighting for his future, sabotages the D.A. who replaced him. Terry and Hildy face an ultimatum about their secret romance.

The murder of a prime suspect in the Normandy Parker case seems to prove Terry's conspiracy theory. Siletti's fragile peace with his family is upended by a ruinous civil lawsuit compounding his legal troubles. And Hildy goes on a date in an attempt to move on from Terry.

Terry and Hildy struggle to collect evidence against their new number one suspect. Terry attempts to repair his relationship with Hildy. The prosecution comes out swinging with an emotional witness who threatens Siletti’s chances at life on the outside.

When a promising new clue is uncovered, Terry and Hildy push forward in hopes of finally solving the Normandy Parker conspiracy. Siletti pulls out all the stops in his crusade against the very system he championed as District Attorney. Hildy’s home life continues to spiral downward as one of her own winds up in the interrogation room.

In this thrilling season finale, Terry and Hildy race to close one of their most complex cases. A new grisly murder hits close to home for the inspectors. Siletti learns his victory in court comes with a substantial price.