Episode 1

A bomb goes off in central London, and people die. The group that claims responsibility is American, and its leader is facing extradition. The group claims responsibility openly, which is its own kind of warning. Their demand is blunt: release him, or crippling attacks will follow at ten-hour intervals. MI5 has a clock it cannot stop, and the whole city is counting down with it. The leader's extradition is the hook the bombers hang everything on. The bomb is the loudest thing in the hour, but the silence between attacks is worse.

The episode runs on that interval, and the structure gives the hour a dread that's hard to shake. Every ten hours the team loses the initiative again, and every lead that goes cold costs time nobody has. The team has to work in the gaps between deadlines, and those gaps are never long enough. And Juliet Shaw, played by Anna Chancellor, arrives as a new presence in Harry's world; the two of them circle each other while the bombs keep ticking. Peter Brooke's Peter, John Chancer's Monroe, Gregory Finnegan's Mark Wainwright, Stuart Sinclair Blyth's Neil, Michelle Bonnard's Delphine Lapin, James Dicker's Wesley Carter, Kelly Clare's coffee shop girl and Will Harrow's university visitor make up the world around the crisis. Peter Firth anchors the whole thing as Harry. Ben Richards and David Wolstencroft wrote it; Antonia Bird directed.

Series four starts in a hurry and doesn't let up. The ten-hour ultimatum is a good, cruel device, and the show uses it properly, letting every false alarm and dead end pile up until the pressure is visible on the team. The opening episode sets its clock and never lets go of it. It sets up the season's themes early, and the setup pays off across the run. It's the kind of opener that reminds you why the series earned its reputation, loud and precise at the same time.