Episode 4

The latest round of Middle East peace talks ends the way the worst-case briefings predicted: a key delegate is killed and the process derails overnight. A diplomat killed at the table sends a message that no press release can walk back. MI5's attention turns to a newspaper mogul with ties to Israeli extremism and the group he is associated with, the November Committee. The mogul is a renowned Israeli extremist as well as a press baron. Two jobs follow. Find out who wrecked the talks, and stop the next killing before it happens, because a pro-Palestinian British MP looks like the next name on the list.

The episode runs on Whitehall time, all quiet meetings and sealed rooms, with the public panic kept at one remove. And the pace is deliberate, the way Whitehall actually moves, and the show trusts that to carry the hour. Caroline Carver's Catherine Townsend and Anton Lesser's Nicholas Ashworth give the politics names and faces worth watching. Lesser, in particular, does menace in a suit better than almost anyone on British television. Jan Chappell's Patricia Norton and Stuart Laing's Richard Hollins fill out the political world. David Oyelowo's Danny Hunter, Richard Harrington's Will North, Keeley Hawes's Zoe, Shauna Macdonald's Sam Buxton and Rory MacGregor's Colin Wells handle the field side. Peter Firth is Harry, holding the pieces together. Ben Richards and David Wolstencroft wrote it; Cilla Ware directed.

Peace processes are fragile machines, and the episode is a reminder that the people who break them rarely sit at the table. MI5 spends the hour running to stand still, chasing an assassination that keeps threatening to land. The most honest thing about it is that the team never quite catches up, and the show doesn't pretend otherwise. The episode ends on a note of provisional relief, the kind that doesn't last.