Andy has tried everything she can think of to get through to her rookie, Duncan, but refuses to give up on him. When a man found shot in stairwell at a dodgy apartment building leads to the discovery of an executed gang leader upstairs, it's all hands on deck at 15 Division to stop a potential gang war from breaking out. Andy and Duncan find themselves alone with the one witness who can tie the killers to the crime; and in a life-and-death moment with a 12-year old witness, Andy may regret giving her rookie so many chances. Meanwhile, Gail follows up on another victim of the tenement shootings - a woman that took a stray bullet in the laundry room - only to make a harrowing discovery that will shake Gail to her core.