After reading a letter from a recently deceased hit-man, Ali connects the murder of an elderly woman to the murders of several informants used in a drug task force Simon ran in the 1980s, and finds out there is an leak within the police force.

Against her objections, Ali is given the job of investigating a doctor whose husband died in a hospice after one of her patients dies under nearly identical conditions in the same hospice.

After a social worker asks Ali for her opinion on a possible child abuse case, Ali looks into the death of a little boy three years earlier in the same household.

After a body is found at a construction site excavation, Ali and Tony look into the case of an Anglican priest missing for two years. Simon asks Ali out on a date after accompanying her to an official function.

Firemen responding to a house fire find a child's picture displayed on a computer. Ali's attention is aroused when the child is identified as a boy who disappeared and was declared dead 15 years before, but in the picture he is older than when he disappeared.

When a young woman claims to have a 17-year-old "recovered memory" of her sister's murder, the whole squad tries to sort through the family's secrets. Meanwhile, Ali attempts to get a confession from a terminally ill man long suspected of being a hit-man.

When an abandoned warehouse is being torn down, a headless corpse is discovered sealed in an interior wall. Tony concludes that the body is an industrialist missing since July 1972.

Ali and Tony check out the story of an informant who claims he knows who killed a tow truck operator in 1991. Their case turns on the testimony of a woman who was a drug addict then, and who is now a hyper-religious housewife.

When a Chinese teenager is found hanging in a jail cell the morning after being arrested, Ali and Tony investigate the similarities with another jail cell hanging 20 years before, when the police department was being investigated for brutality.

When a man comes to the station with a box containing a blood-stained dress with a bullet hole, Ali and Tony investigate a possible murder on the college campus in 1964. They discover the victim wasn't who she appeared to be.

Ali reopens a closed case after she is shown a police video that indicates forensic malfeasance by the lead detective and the profiler.

Ali and Logozzo investigate the murder of retired teacher who, after a stroke, drastically changed behavior.

Ali receives a tip from a lawyer about a young man who had assisted in the rape and murder of three young men years earlier.

As an investigation into a 20-year-old killing spree continues, the Cold Squad is rocked by murder and internal strife.

The 12-year-old case of a murdered woman whose death matches the M.O. of a now-convicted killer. She seems to be another victim of this killer until investigation shows he was in prison at the time of her murder. McCormick and Logozzo try to find who was the original killer and who was the copycat.