Torment

Torment is the strongest single film the series produced, and it earns that position by doing the one thing most of its neighbours cannot: building a mystery out of an impossibility. A prostitute is found murdered in a manner that matches in every detail a series of killings for which Derek Tyler has already been caught and imprisoned. Hill's objection is professional and absolute — in sexual homicides every offender has a unique signature, so this cannot be a copycat — which leaves the question of how the killings are happening at all.

Derek Tyler is the key and the obstacle. He has been mute since the day of his arrest, and every expert who examined him diagnosed paranoid schizophrenia: a man who heard voices and obeyed them. Breaking him requires Hill to use everything he has, and the film's best sequences are the attempts to get a sound out of a man who has decided not to make one. Andrew Westfield plays Tyler as a cipher with a pulse, which is exactly right; the character's blankness is the puzzle.

The answer, carried over from McDermid's novel The Torment of Others, is that the voices were real. Tyler was not psychotic but brainwashed, controlled by someone who used psychological manipulation rather than delusion to make him kill — and that person is now controlling another killer. The film also makes the case personal in the way the series does best: Paula McIntyre is used as bait in a vice operation and is taken by the killer, which is the most serious threat to a regular character the show had yet staged and the reason McIntyre is later described as owing Hill her life.

When it becomes clear that whoever is behind this has access to information about the police investigation, the spotlight falls on someone with a talent for psychological persuasion and a past that explains the motive. The novel names DI Jan Shields, whose compulsion is control, and Siobhan Finneran plays her with an unnerving ordinariness. The vice-squad officer who disagrees with Fielding about how the case is run turns out to be the person running it, which is a more interesting reveal than a stranger would have been.

Guy Burt, who wrote Redemption, structures the film so that the brainwashing and the policing mirror each other: the method used to control the killers is the same method the police use to control people, applied to a criminal end. That is the sharpest statement of the series' institutional theme it ever made, and it arrives without a speech.

It is the highest-rated episode of the whole run in audience polling, at 8.2 from 349 votes, and the reason is not hard to find. It is a single 85-minute story with one killer, one victim chain and no padding, and it demonstrates what the feature-length format could do when the script was equal to it. The one limitation is that the reveal depends on a character the audience has only just met, which is a structural cost of keeping secrets in a stand-alone film. Everything else about it is the show working at its ceiling.