Unnatural Vices: Part 1

The final series opens with a new format and a new adversary. Wire in the Blood returned as four two-part stories rather than single films, and Unnatural Vices establishes the shape of the run: a case that occupies the first hour, and a killer whose interest in Tony Hill runs underneath all four stories. The case is the most explicit the show ever staged, and it begins with a false confession.

A woman is found dismembered and packed into a suitcase. When a young Kurdish woman goes missing, her father confesses to her murder, and the case looks straightforward until it becomes clear that he confessed falsely to protect his daughter's honour. That reversal is a good opening move — the audience is given a solved crime and then told it was a lie — and it pulls Hill and Alex Fielding into the world of sexual sadomasochism, the single element that seems to link a number of gruesome victims.

From there the investigation follows a path the series had used before and sharpens it. The victims were all loners in need of someone to talk to, and the method of torture and death is consistent across them, which narrows the field to a small group: a school teacher, a helpful psychiatrist, and the husband of one of the victims, who models shop mannequins and has a pronounced interest in body parts. A visit to a local S&M club produces useful information from its madam about her regular clients, and the pieces begin to fit.

The episode's most consequential development is collateral. DC Chris Collins, the team's new member, has a girlfriend who disappears, and questions are asked about his involvement — and about how a leather whip he stole from the brothel during the investigation ended up in her flat. Cristian Solimeno plays him as competent and slightly too interested in the work, which is the right preparation for where the series eventually takes him, and the show plants it early enough that the later development is credible rather than shocking for its own sake.

Michael Smiley arrives as Dr Liam Kerwin, the new medical examiner, replacing Mark Penfold's Dr Ashley Vernon, who had appeared in every series since the second. The change is handled without ceremony, which is consistent with how the show treats its own continuity.

What the episode does not do well is restrain itself. The cannibalism is the most deliberately shocking material the series produced, and by 2008 the criticism that had followed it since 2002 — that the violence was gratuitous — had not been answered. The show's response, over six series, was to go further. That is a defensible artistic position, but it is not a neutral one.

It drew 5.93 million viewers and is rated 8.0 by IMDb users. Its achievement is that it sets up a series-long arc while remaining a self-contained first half, and the introduction of Collins and Dr Kerwin gives the final run the two new elements it needed to feel like a beginning rather than a wind-down.