Det. Stillman asks Lilly to re-open a case he couldn't solve, wherein an 8-year-old boy, Tim Barnes, was murdered in 1980. The prime suspects included a catholic priest, three glue-sniffing teenagers, one elusive suspect, and the boy's own parents.

Construction workers discover a skull with bullet hole under the ruins of a disco club burned down in 1978. 22 people died in the fire. Rush and Valens come to the conclusion that the burning of the club was arson, meant to cover up a murder leaving them with not one, but 23 cold cases.

Det. Rush investigates the 1991 double murder of married illegal immigrants from Cambodia who were shot to death in their apartment and found by their 6-year old daughter. The now-teenage girl brings the case to Lilly after she discovers a bracelet once owned by her mother is for sale on the internet. The probe reveals that the parents had dark secrets unknown to their daughter.

After a murder weapon connected to the 1987 drive-by shooting of a little girl turns up, Det. Rush and her team re-open the case. The team slowly tracks back the gun's previous owners until the shocking original owner is finally revealed.

A convicted serial killer will be paroled after 25 years in prison unless Lilly and her team can connect him to the 1977 murder of a young doorman found strangled on a train platform. The killing is eerily similar to other murders committed by the man. Making the case more urgent is the fact that the convicted strangler hints that he will kill again upon release. Elsewhere, Scotty confronts Christina about her past and tries to get her to talk to a New York detective.

When a mother of five loses her fourth son to gang violence, Lilly sets out the save the youngest, reopening one of her first cases on the homicide squad.

When a new witness steps forward, Lilly and the team are prompted to re-open the 1984 shooting of a respected and beloved ER doctor who had a secret he had been hiding from his family.

Lilly re-opens a 2003 case in which an autistic boy's parents were shot in their car when Joseph brings her information that the boy might have seen the killer.

Lilly investigates the 1996 murder of a wealthy divorced woman who was found dead in her ex-husband's indoor swimming pool. The original investigation ruled the death accidental, but new evidence suggests it was a homicide.

The team re-investigates their oldest cold case yet, the 1919 murder of a young woman who was a passionate advocate for women's right to vote.