The programme follows the work of a special police team who investigate "cold cases", which usually concern murders that took place a number of years ago, and were never solved. The team, composed of head officer Detective Superintendent Peter Boyd (Trevor Eve), psychological profiler Dr Grace Foley (Sue Johnston), Detective Inspector Spencer Jordan (Wil Johnson), as well as a number of other supporting characters, use evidence which has recently come to light, as well as contemporary technology to examine former evidence.
Initially, Boyd, Grace and Spence were accompanied by junior DC Mel Silver (Claire Goose), and stern forensic scientist Frankie Wharton (Holly Aird), however both left after the end of the fourth series. Felix Gibson (Esther Hall) and Stella Goodman (Felicite Du Jeu) replaced them in the fifth series, before Eve Lockhart (Tara Fitzgerald) replaced Felix from the sixth season onwards. Katarina Howard (Stacey Roca) replaced Stella in series eight, while Sarah Cavendish (Eva Birthistle) replaced Katarina in series nine. Although the plotlines generally centre around the case, other storylines have been incorporated across the years, including Boyd's anger management issues and being re-united with son, Grace suffering from cancer, Spencer being shot at the hands of one of his former colleagues, and Mel's death, which creates a chain of events lasting across two series.
Trevor Eve stated that the ninth series would be his last, and as such, the series was wrapped up instead of being continued without Eve as the star. As such, The Body Farm, a spin-off revolving around forensic scientist Eve Lockhart (Tara Fitzgerald), was commissioned by the BBC. However, after poor ratings and panned reviews by critics, it was wrapped up after just one series. A total of forty-six stories aired across the nine series.
Detective Superintendent Peter Boyd (Trevor Eve) [Series 1-9] — Boyd is the head of the unit. His involvement in the unit stemmed from the disappearance of his son in the 1990s. Though sometimes appearing detached, Boyd is especially close to his team, and particularly, Mel Silver, whose death haunts him after he is unable to come to terms with it. Boyd's son Luke (called Joe in series 1), a drug-dependent runaway who disappeared whilst living on the streets, was murdered during the seventh series, leading Boyd back to an old adversary whom he put away earlier in the series. As a detective superintendent, Boyd is often stern with suspects, and is unafraid to give them a beating. Boyd appeared in every episode.
Detective Sergeant/Detective Inspector Spencer Jordan (Wil Johnson) [Series 1-9] — Spencer was one of the original officers assigned to the unit since it opened, and soon became Boyd's main sidekick, often joining him in "good-cop-bad-cop" routines in the interview room, and leading the other officers within the team. He was promoted to detective inspector at the start of the fourth series, having initially joined as a detective sergeant. Before joining the unit, Spencer worked for the Atomic Energy Constabulary. Spencer reveals his intention to transfer out of the unit in "End of the Night", but in "Endgame", liases with the unit during his stint in CID, in order to help Boyd track down Linda Cummings.
Detective Constable/Detective Sergeant Amelia "Mel" Silver (Claire Goose) [Series 1-4] — Mel was a feisty, young achiever who worked hard to be promoted from her initial role as constable to sergeant, and who frequently questioned Boyd if she believed he was looking in the wrong direction on a case. She was especially close to Frankie, and the pair soon became best friends. It is revealed that Mel was adopted, as her birth mother was deemed mentally unfit, and that her real name is Mary Price. Mel was killed by a deranged suspect at the end of the fourth series, but Boyd was unable to accept her death until the sixth series, which involves a case she investigated before her death.
Detective Constable Stella Goodman (Félicité du Jeu) [Series 5-8] - Stella joined the unit as a permanent replacement for Detective Sergeant Silver, after being interviewed by Boyd and Grace at the start of series five. Boyd was initially hostile towards her, after being unable to accept Mel's death, but eventually came to accept her. Boyd's trust in Stella was betrayed at the end of series five, when it was revealed she had unwittingly sent information on the unit to her godfather, who had been manipulating her to cover up his own corruption. Stella died at the start of series eight, after being shot in the leg by a suspect she was chasing, and suffering thrombosis as a result of the injury.
Detective Sergeant Katrina Howard (Stacey Roca) [Series 8] - Howard appears at the start of the eighth series as a police constable, formerly a member of the Serious Organised Crime Agency, with a history of insubordination. However, she is transferred into the unit as Boyd's request following the death of DC Goodman. Following the temporary departure of Spencer Jordan, Howard has a much more active role to play within the team than her predecessor, as she is the only other active officer aside from Boyd. Howard did not return for the ninth series, as actress Roca decided to leave the show after just one series. Her on-screen departure was never explained.
Detective Superintendent Sarah Cavendish (Eva Birthistle) [Series 9] - Cavendish was transferred into the unit at the start of series nine, to replace Detective Sergeant Howard, having been moved from counter-terrorism after an incident which led to her becoming the scapegoat. She was one of the youngest superintendents in the history of the Met and, until the incident, a high flyer. At the end of the ninth series, she is murdered by Assistant Chief Commissioner Tony Nicholson, due to her knowledge of his crimes, and by spying on his interactions at The Emirates Stadium with one of the antagonists. Her body was planted in Boyd's shed by Nicholson in an attempt to frame him for her murder.
Dr Grace Foley (Sue Johnston) [Series 1-9]: Grace is a psychological profiler, with nearly thirty years' experience in the field. Her presence in the unit provides a rational counter to Boyd's somewhat unorthodox methods, but the pair enjoy a close working relationship and often engage in witty banter. Grace is often able to build a mental profile of the suspect or suspects, allowing Boyd to break down their mental inhabitants to discover the meaning behind a particular crime or crimes they may have committed. Grace also had a short bout with stomach cancer, which forced her to take time out from the unit to have an operation, from which she fully recovered. Johnston stayed with the programme until its end.
Dr Frankie Wharton (Holly Aird) [Series 1-4] — Frankie, the unit's first forensic pathologist, took a conscientious approach to her job, but remained stern with her colleagues. Frankie was unafraid to speak her opinion, and often offered strong insight into who or what was responsible for the crime. She was good friends with Mel Silver, and it was referenced that she and Mel knew each other before working in the unit. However, traumatised by Mel's death, Frankie chose to leave the unit to return to research, a fact which was explained in the first episode of series five. The real reason for Frankie's departure stemmed from actress Holly Aird, who left the programme owing to her pregnancy.
Dr Felix Gibson (Esther Hall) [Series 5] — Felix took over as the unit's forensic pathologist after Frankie's departure. Felix had already been with the team for some time at the start of series five, and her introduction following Frankie's departure was never explained on screen. Like her predecessor, she would often leave the office to join her colleagues in the field, but took a less stern role within the team, instead offering the knowledge in a more succinct and insightful way. However, she would not hesitate to stand up to Boyd when necessary. The reason behind Felix's departure was never explained on screen, and actress Esther Hall gave no reason for her decision to leave the show.
Dr Eve Lockhart (Tara Fitzgerald) [Series 6-9] - Eve took over as the unit's forensic pathologist after Felix's departure, and her introduction to the team is shown at the start of series six. Unlike her predecessors, Eve practices pathology outside of her time in the unit, and even has her own body farm, which allows her to understand the stages of decomposition in different circumstances from the time of death until as long as five years later. Eve plays a less demanding role in the team than both Frankie and Felix, and instead acts as more of a leader, attracting the team to new cases. Eve also smokes, often in the laboratory, unlike Frankie and Felix. Fitzgerald stayed with the show until its end and went on to revive the character in the spin off series The Body Farm.
The first series secured strong ratings, with "Burn Out" receiving 8.4m viewers and a 38% share. Persistently high ratings meant the programme was recommissioned each year for either the summer or winter schedule. The sixth series began with strong ratings, with "Wren Boys" achieving 9.2m viewers and a 35.2% share. The second part dropped to 8.6m, but still gained a 33% share. Following the successful transmission of the third series and an International Emmy Award nomination for "Special Relationship" written by Stephen Davis and directed by David Thacker, a further two series were commissioned with the number of stories expanded from four to six.Waking the Dead won an International Emmy Award the following year for "Breaking Glass", written by Stephen Davis and directed by Maurice Phillips, and "Multistorey", written by Ed Whitmore and directed by Bob Bierman.