Trial & Retribution III (1)

Fifteen-year-old Cassie Booth vanishes on her paper round, and the case turns ugly fast. Her blood-stained clothes are found on a houseboat belonging to Karl Wilding, a local businessman with an alcoholic wife called Rebecca. Wilding is the obvious suspect, and Walker's team settles in for the usual grind. But Walker's attention is split. Pat North, his partner at home as well as his DI, has been sent to deal with a persistent complainer, and the man will not be shaken off.

That man is Stephen Warrington, a wine merchant who first annoyed the station by reporting a nearby house as a brothel. He is charming and plausible, and far too interested in the case. More to the point, he has noticed Pat North, and she knows it. Warrington, it emerges, lives with bipolar disorder, and his mood swings are frightening when they arrive. Pat gets to see one up close, and the film handles it without flinching: a man who can switch from helpful neighbour to threat in the space of a sentence.

Richard E. Grant plays Warrington, and it is a gift of a part for him, all surface polish with something wrong underneath. Kate Buffery's North carries the weight of it, and the two of them make their scenes crackle. Lynda La Plante wrote it, with Jo Johnson directing. Around them, Michael Simkins' Frank Bradley, Jo Dow's Pete Barrow and the rest of the squad do the steady work, while Candice Mandeville's Cassie, glimpsed early on, hangs over everything.

The clever thing is how the two halves of the investigation start to touch. Warrington's volatility and Walker's prime suspect turn out to have a connection, and the episode ends on that note, with the sense that the polite, watchful man is closer to the horror than anyone realised.