***** S14E01 Mind Games
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Motivational 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. Brody is arrested, but Cassell returns to his office and is found beaten to death the following day. Suspicion falls on millionaire Jason Cohu (Ariyon Bakare) and his father-in-law, Joshua Ray (Joseph Marcell), who blame the men for the death of Jason's wife after her Olympic dreams were dashed by their illegal steroid distribution. 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.

Intellectually disabled convict Carl Meyer (Jonathan Slinger) is released from prison after 20 years of a sentence for murdering his childhood friend, 14-year-old Jane Crewes, though there was insufficient evidence to charge him for the disappearance of her cousin, Harriet Collingham. Carl returns to his home village where the residents are hostile towards his presence, particularly Jane's surviving parent David (Keith Barron), his sister Gloria (Paula Wilcox), Harriet's mother, and her father Charlie (John Castle). When a housing development digs up Harriet's remains, Frost brings in Carl, but is slowly convinced that Carl's protestations of innocence may be true, especially after forensics uncovers that Harriet was likely drowned in the river, and her body re-buried in the woods after Carl was originally jailed. After learning that Harriet had been avoiding her parents and locking herself away, Frost interrogates Charlie, who confesses he was having an affair on the day Harriet died. Frost notices a photo of a boat owned by David and realises the truth: David was raping his niece, Harriet, and killed her to keep his secret. Jane witnessed the murder and he killed her as well, but Carl found Jane's body before David could hide it. Frost confronts David at Jane's grave, but he commits suicide to avoid arrest. Frost drinks over his regrets that if he had not gotten so close to the families he may have asked them more questions, securing justice earlier and sparing Carl a prison sentence, but Mullett reassures him that they must remember their mistakes to avoid repeating them.

***** S14E02 Dead End
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Children's clown Lofty Parker is found dead in an alley. Frost and Toolan investigate and discover that Parker had been stealing jewellery from the homes where he performed, finding a gold ring on his person. Joan Atkins, who hosted his final show, claims that no jewellery is missing, but Toolan finds a ring belonging to a previous victim among Atkins' possessions. This leads Frost to realise that Atkins noticed her rings were missing and told her husband, who then confronted Parker, struck him, and mistakenly took the wrong jewellery back. However, an old head injury of Parker made the blow fatal.

The Heal family is appalled to see Mark Harrison, the man who killed four people, including three members of their family, with his lorry, now driving a local bus. Harrison had appealed his sentence, and his conviction was overturned, with the accident blamed on a fault with the lorry. One night, Harrison and his bus conductress, Jessica Green, are abducted. 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. While Frost was cleared of any wrongdoing, the incident stalled his career for some time.

Green is eventually released by the abductors after they learn she is diabetic and in need of insulin. 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. Trusham tortures Harrison into admitting that the accident occurred because he was distracted by his mobile phone and then throws him into an elevator shaft with a noose around his neck, causing him to land on the elevator.

Frost, Toolan, and Marsh trace Trusham to a condemned office building, where he gives them Harrison's recorded confession and turns himself in. Toolan escorts Trusham out of the building while Frost risks his life to rescue Harrison. However, Trusham convinces the unwitting Toolan to use the elevator, causing it to lower and hang Harrison to death, much to Trusham's delight. With the case closed, Frost credits Marsh for her work, but she admonishes him for risking his life, warning that his rule-bending will eventually be his undoing.

***** S14E03 In the Public Interest
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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. However, Toolan discovers that the men were killed by carbon monoxide poisoning from a faulty heater in cheap accommodation, and the owner buried them that way to make the police think it was ritualistic. The anthropologist was pushing the ritual murder story because she has an upcoming book to promote.

Frost must deal with powerful and wealthy businessman James Callum (Adrian Lukis), whose fitness instructor mistress, Rosemary (Sarah Matravers), is found dead on her houseboat. The profit-focused Callum is bulldozing the local youth club to build offices and has purchased local newspapers, using them to smear his opponents-implicating the youth leaders in a gay scandal that leads one to attempt suicide-and threatens to destroy Frost's reputation as well. Frost interviews Callum's closest associates, his fiercely loyal personal assistant, Michael Carne (Tam Williams), and his long term partner, Michelle, but as he gets closer to the truth, Frost's home is broken into and ransacked, at what he suspects is Callum's instruction. Frost infiltrates Callum's house to learn the truth and discovers that Michelle is the transgender identity of Michael. Michael attempts to kill Frost, but Callum arrives and shoots Michael in the back, killing him. Callum explains that he and Michael loved each other very much, but that Callum's frequent affairs had turned Michael's jealousy into murderous intent, leading to Rosemary's death. As Michael's trial would damage Callum's image and plans, he arranged a situation in which he would be able to kill Michael without punishment. Knowing his confession will be Frost's word against his own, and believing he will be celebrated as an officer-saving hero, Callum contently leaves, unaware Frost has secretly made an audio recording of the entire event.