Needle

A prison warden is run down outside the gates, and nobody needs to be told that he was an unpopular man. The attack has the shape of a message, and Watt is convinced he knows which prisoner ordered it. Knowing who, though, is not the same as proving it. Somewhere out there is the driver, and until Watt finds him, the case is a theory with a victim attached.

The episode's engine is that gap between certainty and evidence. Watt carries the theory, Hawkins and Adler work around him, Evans does the legwork, and the prison provides its own closed world of loyalties and grudges. Frank Mills is the Prison Governor and Godfrey James the Chief Officer Ling, men who have to keep order while the police pick at the seams of their institution. On the other side stand Peter Armitage's Bernie Bryson, Janet Lees-Price's Jane Bryson and James Beckett's Jimmy Cass, the names that keep coming up as the questions get sharper.

Tony Hoare and Elwyn Jones wrote the script, David Sullivan Proudfoot directed, and the show makes good use of the institutional setting. A prison is a stage where everyone has a reason to say nothing, and the writers know it.

The title is a fair summary. The whole episode is a needle hunt, a search for the one small piece of the story that will stitch the rest together. Watt's certainty never quite becomes proof, and that frustration is the point. It is also a reminder that his confidence, usually his greatest strength, is exactly what the case puts on trial. It is a serious, grimly adult hour, the kind of thing the series did better than almost anyone, and it never once lets the audience forget that a man's life has been put in danger by the people around him.