A man is pinned by a train in a subway station, producing a mortal wound that is temporarily suppressed by his situation, the Homicide detectives must determine if the incident was an accident or deliberate.

Bayliss has a new clue on his primary case and with Frank they interrogate a suspect who they believe to be the murderer of Adena

Bayliss and Pembleton are handed "the mother of all red-balls," the stabbing of a judge on the sidewalk in broad daylight. It doesn't take them long to connect Georgia Rae Mahoney's feckless nephew to the murder. But unlike their previous contacts with him, he doesn't go easily this time.

The Homicide Unit takes down the remaining Mahoney organization, but not without collateral damage. Stivers tells Gee that Luther Mahoney's shooting is the reason for all the carnage in the past 24 hours.

Detectives Howard, Bolander and Felton are shot during an ambush and left in critical condition. Pembleton feels obligated to get justice, Munch becomes traumatized and shocked, and Giardello faces an investigation of his work.

A victim was shot in the back, and Frank is eager to find out who done it, however nobody believes him when he states the murderer was a cop.

The unit investigate the death of their friend and Lewis' partner, Steve Crosetti which appears to be a suicide, but Lewis is sure there is more to it than this.

Pembleton and Bayliss look for a gunman who opened fire at a crowded shopping mall, critically wounding a 10 year old boy.

The scene of the crime, Apartment 201, is searched and reveals that the occupant, Gordon Pratt, is a gun freak who once tried to be a cop. A possible suspect is apprehended, but lack of a weapon gets him released. Later, Bayliss returns to the apartment building and is shocked to find that another shooting has claimed another victim. Russert and Howard declare a truce. Still recovering in the hospital, Bolander suffers another relapse.

Felton gets a primary case, in which a family gets robbed and the mother is fatally shot. As the team investigates, the father blames himself for the loss.