Episode 3

DS Steve Arnott is convinced there is a dark secret in Danny Waldron's past, and he is right to be. But while Cottan is commended for cracking the Waldron case, the spotlight swings round onto Arnott himself. His conduct during the Lindsay Denton inquiry comes under scrutiny, and the man who spends his working life investigating other people finds himself on the other side of the table. The interview room looks different from that angle. It is a neat reversal, and the episode does not waste it.

The episode does something the series is good at: it turns the investigators into the investigated. Arnott's certainty about Waldron starts to look like a man who knows the shape of the thing because he has seen it up close. Around him, Fleming, Brickford, Bains and McAndrew keep the machinery turning, and Hastings watches it all with the expression of a man who has seen this before. The suspicion is thick enough to walk through, and everyone in the building is breathing it. The show has always understood that suspicion is a contagion, and this hour is a demonstration.

Jed Mercurio wrote it, Michael Keillor directed. Martin Compston plays a man carrying the weight of his own past, and Daniel Mays keeps Waldron's secret coiled under the surface. Vicky McClure's Fleming, Leanne Best's Brickford, Arsher Ali's Bains, Lisa Palfrey's McAndrew, Adrian Dunbar's Hastings, Craig Parkinson's Cottan, Maya Sondhi's Bindra, Jonas Armstrong's Nash and Melissa Dean's care worker complete the cast. It is a deep bench, and the episode uses it well.

It is satisfying when a procedural turns on its own people and lets the ethics get messy. Arnott's past behaviour is not excused, and it is not ignored. But the episode simply lays it out and lets it sit there. The two stories are running on the same track, and the collision is coming. Whatever is buried in Waldron's history, Arnott may find his own buried alongside it.