A former high line thief from Boston tries to give up crime for the sake of his teenage son, and Mary and Marshall search for the person who nearly killed Mary in the season two cliffhanger.
After being discharged from the hospital with a fresh bullet wound scar, Mary gets right back to work with Marshall. They come across what appears to be video footage of an armed robbery that looks suspiciously similar to the robberies that one of their witnesses used to orchestrate as a mobster in Boston. The witness: Jimmy McCabe.
After grilling McCabe, Mary turns her attention to Jimmy's sons who are doing their best to conceal the truth about their dad.
Meanwhile, Marshall’s presence in gangland is starting to hurt gang-banger Lala's business. But Marshall is looking for the name of Mary’s shooter. It's only a matter of time before Lala's proximity to the cops ruins his business, and before Marshall gets in too deep.
Jinx doesn't provide the warmest homecoming for Mary when she blames her for putting the family through hell while she was in the hospital. Also, Peter begins to suspect that Brandi's mysterious phone calls aren't as innocent as she's making them sound.