Len has a suspect delivered to him at an abandoned shelter in the forest in order to coerce a confession out of him. Ali and Mickey question a former teacher at Ambleton about the murder of two children there.
Mickey tries to convince Harper and Pawlachuk that a pile of old letters holds the key to a teen-aged girl's murder. Ali teams up with a Russian cop to connect stolen Russian historical documents to a murder.
Christine's brother Aaron dies after being hit by a car, and she presses for a murder investigation. When that doesn't happen, she infiltrates a group of car street racers without authorization. Len and Ali investigate the death of an infant.
Len and Nicco work with a homicide detective to look into the connection between a cold murder case and the more recent murder of a gay-bashing thug at the same night club. Mickey uses a new computer program to find an arsonist.
A former homicide detective, who was demoted to beat cop 15 years ago for publicly hanging a suspect off a bridge, is promoted to the Cold Squad. He and Nicco work on the case of a body found encased in concrete of a building under construction.
Len meets the "victim" of one of his old Homicide cases . . . alive . . . in the holding cell. Mickey is confronted with new developments in a cold case involving a 4-year-old girl, whose decapitated body Mickey found when she was a patrol officer.