Episode 4

Mohammed Khordad is the number three man in al-Qaeda, and he wants a meeting with MI5. Under any normal circumstances the answer would be no. But Harry Pearce convinces the team that any chance to reduce the threat of attacks has to be taken, however dirty the meeting feels. It is a considerable risk, taken in pursuit of what might be peace. The team is stunned by the approach, and the meeting itself is the kind of thing that would end careers if it leaked, which it inevitably will.

Khordad keeps his cards close. He insists they must trust one another before they can deal, and then he puts it to the test: a bomb will go off at 3 pm that afternoon unless the Home Secretary publicly absolves two suspected terrorists of any wrongdoing. Do that, he says, and he will have something more important to offer. The team races to find the bomb while Harry works on the Home Secretary, and the CIA hovers in the background with its own interest in Khordad. There is no way to verify anything he says, and the hour leans into that, making every decision a leap.

Richard McBrien wrote it, Peter Hoar directed. Peter Firth plays Harry Pearce, with Hermione Norris's Ros Myers, Richard Armitage's Lucas North, Miranda Raison's Jo Portman, Gemma Jones's Connie James, Hugh Simon's Malcolm Wynn-Jones and Alex Lanipekun's Ben Kaplan around him. Guy Henry is Sam Stevens, Rohan Siva is Aram Beyda and Robert Glenister is the Home Secretary.

The episode is a bargain with the devil conducted in real time, and the show is smart enough to make the devil seem reasonable. Khordad speaks sense, which is the most unsettling thing about him. Everyone in the room is doing arithmetic on other people's lives, and the episode lets you watch the sums. Whether the deal is worth it is left hanging, which is the right call. Some questions should stay open. And the bomb, whatever happens with it, is only the opening bid.