Episode 2

A plague hits London, and that is the whole episode. A virus is loose in the city, the death toll could reach half a million, and Section D's job stops being counter-terrorism and becomes triage: find everyone who might be infected, quarantine them, and do it without starting a panic in the streets.

The officers work the chaos of an outbreak while trying to keep some semblance of order among the public, and the mission splits in two: contain the infected, and keep the rest of the city from running. When the source of the cure stays out of reach, held by allies who may not be forthcoming, Harry Pearce orders the team to take extreme measures to secure the antidote.

The hour then spends itself watching decent people decide how much of their own rulebook they are willing to tear up. Adam Carter, Ros Myers and Jo Portman are caught between institutional protocol and the simple necessity of acting, and the strain shows. Nobody has time to ask what the state will look like once it has learned to dose the city in an emergency.

Neil Cross and David Wolstencroft wrote it, with Omar Madha directing. Peter Firth anchors as Harry Pearce, Rupert Penry-Jones as Adam Carter, Hermione Norris as Ros Myers, Miranda Raison as Jo Portman, Hugh Simon as Malcolm Wynn-Jones and Gemma Jones as Connie James. Matthew Marsh's Bob Hogan, Agni Scott's Ana Bakhshi, Simon Abkarian's Dariush Bakhshi and Ulas Kilic's Mehan Asnik round out the cast.

The scariest thing about the hour is how quickly the machinery of the state starts to look like the threat itself. But everyone behaves sensibly and the situation still goes bad. It is a reminder of how fast a city can come apart when the enemy is invisible. The plague never gets a face, which is the right choice. The people are the disaster.