Background enquiries turn up two previous deaths, which appear related to the case. But their initial suspect, armed bank-robber Charlie Lehman, turns out to have died in prison over a year earlier. As they work to profile the killer they are hunting, Frost starts to get close to Hartley personally as well as professionally, though neither realises just how closely she is linked to the case until it is almost too late. Frost has a race against time to find where she is being held.

A man is released on licence after serving 20 years for the murder of a 14-year-old girl. When the body of her best friend, who disappeared at the same time, is found, Frost has to investigate a 20-year-old murder.

Frost investigates an MP's son who is involved in a hit-and-run accident, and a robbery at a private casino, which occur on the same night. He gets a humorless new partner to assist him.

A body with no identification is found in a local reservoir, and a couple fall victim to a brutal killer in their own home. Frost is assigned a new, female, West Indian detective constable, Ronni Lonnegan, and gets off to a bad start with a few racially-insensitive remarks. He then reluctantly accepts the help of a psychological profiler, psychiatrist Pam Hartley, who he met at a conference. Meanwhile, there is an inspection of Denton Police underway, and Frost's old-fashioned methods are not endearing him to the inspector, so Supt Mullett is forced to give him more support than usual.

The body of Lemmy Hoxton, a small-time burglar, is found at an abandoned farm. There is a spate of break-ins where the intruder gives the sleeping children injections, which reminds Frost of a similar series a few years earlier. A man returns home late one night to find his children dead and his wife missing. Frost's investigations make as many demands on his compassion as on his professional expertise, and he makes a serious error of judgement.

Frost investigates two domestic cases. The first is the tragically straightforward murder of a cantankerous old man by his wife. The other is a more cruelly deceptive one, in which a man is killed, and his son and one of his daughters go missing: Frost tracks them down to Blackpool, where she has gone for an abortion - but who was the father? The answer leads him and DS Barnard into a tragic confrontation with an armed and dangerous paedophile.

Hazel Wallace returns from her training, as the new Detective Sergeant, and is put to work by Supt Mullett sorting out the mess left behind by DI Frost, while he is on extended compassionate leave. Before long she is called upon, when a man is found hanged in his home, and she suspects it was not suicide. Routine investigations show that a fresh set of fingerprints at the scene belong to an unidentified man who had been found drowned a year previously. Frost is summoned back by Supt Mullett to sort things out, and he connects a painting that appears to have been stolen from the hanged man with an art robbery & murder some years before.

Frost investigates two deaths: a homeless teenage girl, found beaten up and drowned in Denton's river; and that of an environmental health officer, after a dismembered arm is washed up on the shoreline. This leads to the investigation of a local meat processing factory.

With the railroad murder solved, Frost tries to come to terms with having an previously unknown daughter. Detective Reid is sent to look for contraband cigarettes, but is found nearly dead on a public toilet. Was he high, or did Frost´s lookalike have anything to do with it? Meanwhile, Frost eliminates suspect after suspect in the surgeon murder, and ends up saving several lives.

A vital witness to a gangland killing goes missing before she can give evidence in court, And frost finds himself under pressure to find her and her son before a hitman can get to them. Frost thinks he has won the lottery but he has lost his ticket!

DI Frost pursues a paedophile suspected of abducting a 10-year-old boy from a Denton Town football match. Initially, Frost is unsure whether the lad simply ran away or is genuinely the victim of a kidnapping, but when the boy is found dead and a man is found dead following a hit and run incident, the identity of the latter creates a frightening link to the missing child. When a second child turns up dead in a deserted quarry, Frost is in a desperate race against time to stop a third child being murdered. While Frost is contending with this a note arrives from a secret admirer and Mullet tries to push Frost into a promotion he doesn't want.

The murder of a widow soon gives Frost a chance to prove his worth again, but the investigation only reveals an intriguing web of deceit, and it isn't until a forensic psychologist joins the team that they realise a serial killer is at work.

The first in the final two-part episode in the series sees Frost attempting to crack an illegal dog-fighting ring, only to discover that its manager, a wealthy Denton businessman, has links to a drug-smuggling operation. Frost also begins to form a relationship with RSPCA Inspector Christine Moorhead, and attempts to finally get over the death of his wife.

Frost considers retiring from the Police force and plans to get married, ending the series, however DS George Toolan dies of heart failure following a collision outside the church where the wedding is about to take place. It is noteworthy that an alternate ending was filmed, where Frost is killed instead of George, but David Jason chose the 'happier' ending over this one.

Nursing his terminally-ill wife, Det Insp ""Jack"" Frost's life becomes more stressed when, during a missing-child investigation, he unearths evidence on a 30-year-old case involving a skeleton chained to a locked strongbox that turns out to be empty.

Frost investigates the murder of a teenage girl, and the case of a woman who has been receiving threatening phone calls. Meanwhile, at the Denton police station, there are threats, deaths, arson and a staff shortage.

Frost's house is burned down, and he moves in with a colleague temporarily. A mysterious, ruthless kidnapper on a motorcycle tests Frost's skills to the limit. It proves a tough case to crack, and for the abducted woman, time is running out.

Frost continues to try to identify the detective's killer. The task is complicated by a bizarre series of pet shootings, about which he is reluctantly forced to seek help from a computer system run by a seconded new junior WPC. His pursuit leads to a confrontation high above a power station.

Frost's Christmas is overshadowed by a local power station worker falling to his death in a mysterious accident, shortly after he was burgled. Then a young police detective, Tim Fox, is murdered, and Frost wonders if it really is related to the large investigation he was working on to uncover a car theft gang.

Frost investigates a series of break-ins and brutal attacks at the homes of elderly people. He is helped by a female detective, DS Lawson, who also offers him advice on his personal life.

An 8-year-old girl is missing, and the last person to have seen her is Billy Conrad, a gentle young man with Down's syndrome, but who appears is hiding something.

A young woman is found viciously stabbed to death. Frost consults the victim's personal organiser, from which a trail leads him to a religious community.

A sub-postmistress is fatally stabbed in a small-scale robbery, and Frost wastes a lot of time questioning the leading suspects. Then, Helen Tudor, a beautiful first-year psychology student and keen swimmer at Denton University, is attacked on the campus, and suspicion initially falls on her psychology tutor, Keith Michaelson, but Frost's investigations uncover a link with the death of another beautiful young girl swimmer two years earlier, in another town.

Frost is held at gunpoint by a drugs dealer, a Territorial soldier is shot dead on an exercise, and a security van is robbed by a shotgun-wielding gang. Frost investigates the three incidents, and tries to find any links between them. His intrusions onto the army base stir up hostility from the commanding officer.

Frost responds to a call for help but, when he arrives at the scene, all he finds is a disembodied leg… and a crocodile!