Episode 2

The plot against the government survives the first round. MI5 foils an attempt to murder the Home Secretary, but the plotters are already on their next move. Using the very emergency powers passed in the wake of the attacks, they imprison Harry Pearce, and the team is left with a deadline: frustrate the coup before Harry is executed.

Juliet Shaw is coming to terms with her own injury, which gives the episode its quiet counterpoint. The Service is coming apart at the seams while its people recover, and Anna Chancellor plays Juliet with a sort of furious patience. The injury keeps her off the front line, and the episode is quieter for it. Robert Glenister's Home Secretary is the polished face of the other side, all reassurance and no answers.

The conspiracy, the team slowly realises, reaches much further than anyone first assumed. What began as a handful of extremists has become an elite group with its eye on the whole country, and every arrest takes them closer to somebody more senior. The episode has the quality of a screw turning; you can feel it tighten every ten minutes.

Ben Richards and David Wolstencroft wrote it, Omar Madha directed. Peter Firth's Harry sits at the centre of the storm, with Anna Chancellor's Juliet, Rupert Penry-Jones's Adam, Raza Jaffrey's Zaf, Steve Nicolson's Steve Jensen, Hugh Simon's Malcolm Wynn-Jones, David Phelan's Air Traffic Controller, James Cash's Conspirator and Mark Straker's Manager around him. It aired the night after the season opener.

And there is something properly chilling in watching the machinery of emergency law turn on one of its own servants. Harry locked up by the powers he helped enforce is the season's argument in a single image. It is the rare episode where the villain is the system itself, and the show has the courage to keep it that way.