A petty crook, Ricky (Tim deZarn), hoping to get a reduced sentence, relates witnessing a young man washing blood out of his car the night a teen track runner was cuddled. The young athlete, Paige Pratt (Summer Glau), was found shot, and her boyfriend Al Clarkson (Doug Kruse) was originally imprisoned for the crime.
Lilly Rush, the lone female detective in the Philadelphia homicide squad who finds her calling when she's assigned to "cold cases" - crimes that have never been solved.
Previously, she used her instinctive understanding of the criminal mind on current murders. Now, she's interrogating witnesses whose lives and circumstances have since changed, making use of today's new science and finding fresh clues to solve cases that were previously unsolvable, all of which appeals to this smart, driven detective.
She's also prepared for the consequences: that her work will open up old wounds and may lead suspects to commit new crimes.
When she hits a dead-end, Lilly seeks advice from her respected mentor, Lt. John Stillman. Also on the team are Det. Scotty Valens, Rush's confident and strong-willed partner; Det. Will Jeffries, who's been around long enough to serve as Lilly's link to the past; and Det. Nick Vera, a tough cop who's considered the go-to guy for getting a confession. Lilly makes it her business to ensure that no victim is ever forgotten. On the show's third season, former narcotics detective Kat Miller, a young and spunky girl, joins the team.