21 is the number of bridges in Manhattan. Andre Davis (Chadwick Boseman) is a top NYPD detective who uncovers an unseen conspiracy against cops. In a battle of life and death but without having any clear idea who the enemy really is, Detective Davis locks down New York City to help police catch a gang of cop killers. Tough times require tough measures. The authorities close all the 21 bridges that connect Manhattan to other New York City boroughs, so no-one could go out of the island or enter it. In pursuit of unknown criminals, Detective Davis gets the awkward feeling that someone is actually pursuing him.