Finch gets the number belonging to Charlie Burton, a high school history teacher in Brighton Beach, Brooklyn, and an unlucky witness to a Russian mafia murder. Reese, with no time to spare, rushes to Charlie's side and whisks him out of danger just as the mob descends on his apartment to silence him for good. But they can't shake the Russians that easily. In hot pursuit, the shooters chase them into the infamous Double B High Rises -- a city housing project that has fallen into disrepair and is now home to thugs and illegal enterprises. Reese must find a way to escape the Double B's with Charlie and get him safely across the river into Carter's hands so that Charlie can testify to what he saw and bring justice to the victim of the murder. But the mafia is dead set on killing Charlie and will stop at nothing to make sure that Charlie doesn't make it out of the Double B's alive. And when Reese loses contact with Finch, Finch must look to Detective Fusco for help.

Reese and Finch's game of cat and mouse with Detective Carter becomes infinitely more complicated when The Machine declares that she is their newest POI.