Trial & Retribution XX: Siren (1)

An ambulance, forced off the road by gunmen. That's a bold opening even by the standards of a show that has never once been accused of restraint. A paramedic dies in the crash. Then the gangsters walk up to the overturned vehicle and shoot the patient, Sebastian Cole, in the head. Whatever Cole was involved in, it was serious enough that nobody intended to leave him for the courts.

The shape of it emerges quickly: Cole and his friend Ross were running drugs, which is the sort of secret that tends to end this way. The police work gets complicated in a very human direction when DCI McGill turns up furious, because Mike and Roisin have just barged in to interview Ross while McGill had him under his own surveillance. Two investigations, one informant, zero cooperation. Vincent Regan plays McGill as a man more wounded by the trespass than worried about the case, and it's a genuinely funny bit of friction in an hour that otherwise doesn't do funny.

Then there's Imogen, Cole's girlfriend, an It girl who lives in the tabloids and grieves for them too. Her mother tells the police her daughter knew nothing about any of it, and the team's collective expression suggests exactly what they think of that. Tamsin Egerton gives her a brittle, photographed quality; she's distraught the way people are distraught when they know cameras are present. But the team needs proof, not instinct, and proof takes its time.

Damian Wayling and Lynda La Plante wrote it, Julian Holmes directed. Hayman, Smurfit and Lough hold the centre as Walker, Connor and Satchell, with Caroline Loncq as DS Ellis, Michael Thomas as Patterson, Joseph Kennedy as Sebastian, Fiona Mollison as Tanya and Gary Cady as Randall.

A strong start to the final series. The question isn't who killed Sebastian Cole, since we watched it happen. It's how far the rot around him goes.