Season 4

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 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.

A woman commits suicide naked in public, and Frost connects her death with the later death of a gigolo. He discovers that the dead man had business with several women in Denton. Meanwhile there appears to be a series of break-ins at the local cricket pavilion, and Supt Mullett, who is a member, orders Frost to investigate them as well as the murder.

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.