Owen takes the lead on a murder investigation involving the brother of his former criminal informant who was killed a few years before. Meanwhile, Clark struggles with whether or not to let his recently sober mother back into his and Agnes' life.

McKenzie seeks justice for her family when bullets found at the scene of a subway shooting match the same gun that killed her brother several years earlier. Meanwhile, Owen has reservations about retiring in two years.

When Clark is relegated to desk duty, he delves into Owen’s cold case in which the murder investigation of a construction worker was compromised by the events of 9/11. Meanwhile, Deputy Mayor Holbrook pulls a gun on Clark and Margot, Agnes drives away with her father, and Owen gets his long deserved promotion.