The Harrowing (3)

The body count climbs and Red's composure goes with it. He has been chasing patterns and connecting deaths, and none of it has delivered a face to arrest. The frustration is written all over the investigation, and the episode doesn't rush the payoff. Then it clicks. Isabel. She has been there the whole time, and she is the key the investigation was missing. There's no drumroll for the revelation. It arrives the way these things usually do, as a tired realisation in the middle of a long night.

Professor Robb steps in as the guide Red needs, helping him move past the what of the crimes to the why. It's an unusual kind of help for a detective to accept, closer to philosophy than procedure, and the show lets it sit rather than rushing past it. Red has spent this story being pushed to the edge of his sanity. But understanding, when it comes, is offered as a kind of rescue. Robb's lectures are the calmest thing in the hour.

Around him the team keeps working. Warren and Vickie Clarke chase the leads, Rachel Price reads the dead, and the Eccleshall and McArdle families circle the investigation with their own claims and secrets. Theories that looked solid through two episodes turn out to have been built on sand. The pieces fit together at last, which is not the same as saying anyone gets comfort from it.

Terry Cafolla and Boris Starling wrote it, Paul Unwin directed. Ken Stott, Neil Dudgeon, Maxine Peake, Helen McCrory and Harriet Walter carry the main weight, with Hugo Speer, Adam Kotz, Beatie Edney, Margot Leicester and Eamon Boland in support.

It ends the season on a strange, thoughtful note. The killer is understood. That doesn't make the deaths easier to carry, and the show doesn't pretend otherwise. For a season this dark, that counts as a mercy.