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.

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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.