Cherubim and Seraphim

Cherubim and Seraphim, written by Julian Mitchell and directed by Danny Boyle, is among the most personal stories the series ever told, for the dead girl at its centre is Morse's own niece, Marilyn Garrett. A spate of teenage suicides has been loosely tied to the local rave scene, and when Marilyn is found to have taken a massive overdose for no reason anyone can supply, Morse takes leave to investigate her death unofficially, unable to bear the idea of strangers handling the file.

The case pulls him into a world he barely comprehends: the acid-house parties, the strained families, the gap between what bereaved parents believe and what their children lived. Sorcha Cusack's Joyce Garrett, Marilyn's mother, carries the episode's grief with a rawness that anchors its stylish surface, while Jason Isaacs's Dr Desmond Collier, a pathologist drawn to the scene, and Liza Walker's Vicky Wilson, another of the lost, widen the picture of a generation slipping through adult fingers. Isla Blair's Janey Wilson gives the bereaved-parents' network a fierce, organisable fury.

Meanwhile Lewis, studying for his inspector's exam, is temporarily attached to a rigid, by-the-book officer who could not be more unlike Morse, and the parallel tracks — the maverick uncle and the rule-bound sergeant — sharpen the series' perennial argument about what good policing actually is. Boyle, years from Trainspotting, brings a pulsing, kinetic energy to the rave sequences that makes the quiet domestic scenes more desolate by contrast. The resolution is quietly devastating: not a killer to be caught but a void to be acknowledged, and Morse, who solves everything else, is left with the one mystery his intellect cannot master. Morse's stepmother Gwen, played with wary fortitude, and Joyce Garrett's grief, frame the case as a family matter the chief inspector is unequipped to handle, and his uncharacteristic helplessness is the episode's emotional core. The rave scenes, pulsing and alien, are cross-cut with the silent rooms where parents wait for children who will not come home, and Boyle makes the distance between those worlds the whole point. Dr Collier's professional detachment and Vicky Wilson's survivor's guilt sketch the outlines of a youth culture the older characters can only police, never understand. By the end Morse has established not a culprit but a pattern — a string of overdoses that the authorities prefer to file as accidents — and his refusal to let Marilyn's death be one more statistic is the most personal act of justice the series ever grants him. The episode is a eulogy disguised as a police procedural, and all the more powerful for it. The rave, for all its noise, is finally quieter than the silence in the Garretts' house, and Boyle lets that silence have the last word.