[1] No-nonsense detective inspector, Jack Frost, is caring for his terminally ill wife when he is forced to assume command of an investigation into the disappearance of a young girl, Tracy Uphill, aided by DC Clive Barnard, the Chief Constable's nephew.
DI Frost finds himself coping with a shortage of officers, due to an illness circulating the area, and the sudden arrival of his late wife's overbearing sister, as he handles two investigations.
DI Frost investigates a series of burglaries directed against old age pensioners, assisted by new female DS Maureen Lawson (Sally Dexter), eventually tying them to non-violent burglar Bernard Elliott.
Frost concludes that the second victim knew her attacker and let them in to her home, and learns from her neighbour that, Ronald Gould, a driver for the bus to her regular bingo game, had offered to replace the broken chain on her door.
He is reunited with DC Clive Barnard, as he finds himself investigating the murder of Nick Walder, who was struck over the head from behind while assisting a group in sabotaging a fox hunt by wealthy locals.
He has a stressful day, first held at gunpoint by young drug dealer Steve Marson, and later learning that soldier John Meredith has been shot dead during a firearms exercise at a local army camp.
However, when Captain Carlisle from the Special Investigation Branch takes over, he finds that the bullet was Russian-made, suggesting an external shooter and turning it into a murder case, giving Frost jurisdiction.
He learns that the business owner is selling the company and denying redundancy pay to the drivers, including older staff members Les James, Barry Hockey, and Dave Chaplin.
Meyerbridge's defense is led by Edward Gull, a solicitor and influential member of the local religious community who also holds a key position on the board managing public and police affairs.
At the same time, Frost and Nash investigate a series of smash-and-grab robberies in Denton's commercial district, in which the thieves manage to steal large quantities of goods and escape within minutes.
Working alongside WPC Lindsey Hunter (Katrina Levon), Frost investigates and an assault on Helen Tudor (Tamzin Malleson), a beautiful and sweet-natured student at Denton University, who was pushed down the stairs following a private tutoring session, and can recall someone asking her not to die there.
With help from DS Clive Barnard (Matt Bardock), now based in Boxborough, Frost learns that Paula Tate, a victim who looked similar to Helen and was also an avid swimmer, drowned there 2 years earlier in an apparent suicide.
DI Frost is forced to cancel his holiday plans to investigate the suspicious death of a young boy, Dean Anderton, on Halloween, working alongside the ambitious DS Liz Maud (Susannah Doyle).
Sheridan is given an alibi by his infuriated wife, while Frost meets with local priest, Father Sullivan (Eoin McCarthy), who recently heard confession from someone claiming they were going to commit murder.
Meanwhile, DI Frost moves into a new flat, and allows his old partner, DS Clive Barnard, stay with him while they handle investigations into an armed robbery at Peter Lawson's (Mark Lambert) pawn shop, and a separate murder involving elderly married couple, Harry and Olive Walters (Jean Heywood).
Frost learns that Olive's actions were impulsive, the result of decades of emotional abuse from her husband, whom she held responsible for the death of their 2-year-old daughter nearly 40 years earlier, because he refused to let her go to hospital to treat her fever.
Without Jane's testimony, Frost is unable to prove Deering beat her and is forced to release him, but vows to pursue kerb crawling charges and ensure the case is covered in the local press to publicly shame him.
Frost solves the Sylvia Carter case after learning she was indeed accidentally hit by a train while crossing the tracks with her affair partner, who hid his involvement out of fear of his wife taking his children.
There are three prime suspects: Jameson, whom she was going to expose for corruption if he did not improve her department funding; Dr. Retnik (Frank Kovacs), whom she wanted to resign because she believed he was responsible for the high number of unexplained deaths in Bed 5 of the ward; and James Ingram (Bill Fellows), the father of a young boy who died following surgery overseen by Gibson.
While Superintendent Mullett and the Denton station prepares for the arrival of Babcock (Michael Cochrane), Her Majesty's Inspectorate (HMI), which will determine their future funding, Frost and a new CID team member, DC Ronnie Lonnegan (Michelle Joseph), investigate three murders: an unidentified body found in a reservoir, and the deaths of Jean and Paul Harris, who were bound, doused in petrol, and burned alive.
Frost is tasked with protecting Cathy and her young son, Robbie, until she can testify against Flynn, and requests DS Terry Reid's assistance owing to his connections with the Metropolitan Police in London.
Frost and Detective Sergeant 'Razor' Sharpe (Philip Jackson) lead the investigation, and psychological profiler, Dr. Martine Phillips, surmises they are dealing with a serial killer who derives sexual gratification from killing.
Helen's autopsy reveals she had aborted a child several weeks earlier, casting suspicion on her alcoholic ex-boyfriend, Steve Markham (Jeff Rawle), and Frost discovers that her sister, Sylvia Ford (Lia Williams), is having an affair with Rose.
After another victim is found, Frost deduces that Helen was trying to indicate who killed her by reaching for her locket, which was a gift from Sylvia's religious husband, Bill (Mick Ford), and purchased from Markham.
Motivation speakers, Roman Cassell (Dhafer L'Abidine) and Tom Brody (Vince Leigh), are tricked by their lovers into disrobing for a midnight swim, at which point the girls run off with the men's clothes, leaving them to streak through Denton.
Frost deduces the lack of blood at the scene exonerates Jason and Joshua, but discovers that one of the women, Babs Sellwood (Elizabeth Berrington) was in an abusive relationship with Cassell, and when he mocked her and threatened to tell her children she was a slut, she snapped and struck him over the head, killing him.
Frost works the case alongside DS Annie Marsh (Cherie Lunghi), who once reported him for dereliction of duty after he pursued a knife assault suspect without backup, leading to an officer being injured.
Frost identifies an inconsistency in the alibi of the Heal's youngest son, who confesses that he and Robert Trusham, the husband of the fourth victim, abducted Harrison to teach him a lesson, with Green being an unfortunate bystander.
The naked bodies of three Eastern European immigrant workers are found, arranged in a triangle, in a grave at an old burial site, and an American anthropologist insists to Frost that these are ritual killings.
Frost and his team assist RSPCA officer Christine Moorhead in dismantling an illegal dog-fighting ring, but its organiser, drug lord and money launderer Gerry Berland, avoids arrest after a delay makes him arrive after the police raid.