

Witness testimony, even from people who would later be revealed as the killer, was almost never false. These interviews were accompanied by flashback sequences to the time of the murder which dramatized the testimony.

Over the course of the episode, the detectives would interview witnesses associated with the crime and piece together the story of what led the victims to their death. In some cases, the lack of a body meant that it was originally unclear if a crime had even occurred, with people instead believing that the victim had merely left town. This might be the discovery of a body, a new lead such as an alibi witness not found in the original investigation, new evidence pointing to the innocence of the accused, or a critical piece of evidence such as a murder weapon (e.g., one investigation began when a gun received in a gun buyback program was linked to a murder through ballistic evidence). Generally, an investigation would begin when the police received a new lead, or "new direction", on a case. Cases were also spread out over much of the previous century, with some as recent as a year or two old and others dating back to the 1910s. All cases involved murders committed in Philadelphia, although investigations occasionally required travel outside the city. Usually, each episode would focus on a single investigation. They work under Lieutenant John Stillman ( John Finn) and are assisted by other detectives from their squad-Nick Vera ( Jeremy Ratchford), Will Jeffries ( Thom Barry), and beginning in season three, Kat Miller ( Tracie Thoms). Rush was initially partnered with Detective Chris Lassing ( Justin Chambers) in the first five episodes and then with Detective Scotty Valens ( Danny Pino) for the remainder of the series.

The show is set in Philadelphia, Pennsylvania, and follows Detective Lilly Rush ( Kathryn Morris), a homicide detective with the Philadelphia Police Department, who specializes in "cold cases", or investigations which are no longer being actively pursued by the department.
