Dancing in the Dark

A man's corpse is found on a waste tip, stripped of everything bar his clothes and an empty wallet — the signature of a mugging, except nothing about it sits right. Frost, working alongside the cocky young undergraduate DC Jasper Tranter, pieces together the story of Joe Hawkins: an absent, abusive, alcoholic husband whose meek wife Dianne had fallen in love with an equally meek sleep therapist, Colin Bayliss. Their plan was to take money from the sleeping Joe and run away together. Joe woke, began choking on his own vomit, and the panicking couple smothered him, dumping the body to look like robbery. Whether Joe died of the choking or the smothering is unclear — and Frost is left unsure if either of them will ever be convicted. It is the kind of case the series loves: a murder that is also a mercy, a crime that the law cannot quite get its hands around.

The second case is a tragedy wearing silk. A young escort, Heather Wills, is found dead in a hotel room registered to Stephen Richford, a wealthy businessman and close family friend. Richford had booked an escort and been horrified to discover it was Heather, his daughter's best friend, who set about seducing him for money. Guilt-ridden, he is later discovered dead in what looks like suicide; Heather's ransacked flat yields the real secret: forged passports hidden in her purse, used to smuggle women into the UK, which she was holding back from her boss until he paid her more. The boss is involved, but the killer is his ruthless partner, Terry Hirst — who killed Heather and staged Richford's suicide to frame him for her murder. Frost draws Hirst out with a sting at a greyhound track and arrests him.

Dancing in the Dark, written by Christopher Blake and directed by Roy Battersby, is the series at its most lurid — pole dancers, false passports, a dead girl and a dead tycoon — and its most melancholy: two cases, two couples destroyed by the secrets they kept. Nicholas Burns' Tranter, all undergraduate swagger, makes a fine foil for Frost's exhaustion, and the episode's title is the show's own theme: everyone in Denton is dancing in the dark, and Frost keeps turning the lights on.

Lurid and melancholy in equal measure, Dancing in the Dark gives the series one of its most tangled plots and its best undergraduate foil in DC Tranter. Lurid, melancholy and utterly absorbing.