Episode 5

The death of Samuel Walker, the CIA station boss, is ruled a suicide, and Harry Pearce refuses to believe it. Suicides in his line of work are always convenient, and this one is convenient to the wrong people. When another CIA agent turns up dead, he starts connecting the bodies to something bigger: a power meeting being held in Basel. The pattern is there if you look at it sideways, and Harry has spent a career looking at things sideways.

The case lands close to home when Ros's old mentor, Jack Coleville, gets in touch. The reunion is not the warm thing it should be, because Coleville is clearly tangled up in whatever is happening, and Ros ends up in the firing line trying to prove who killed the two agents. It is a reminder that in this world the people who trained you can become the people you have to take down. Jack Coleville is one of those names from the past that never stays in the past.

Richard McBrien and David Wolstencroft wrote it, and Alrick Riley directed. Hermione Norris's Ros carries the centre of the episode, with Peter Firth's Harry piecing it together behind her. Genevieve O'Reilly's Sarah Caulfield, Richard Armitage's Lucas North, Nicola Walker's Ruth Evershed and Shazad Latif's Tariq Masood support, and Wade McElwain plays Michael Braydon, with Callum Marullo and Charlie Graff as his two boys. Robert Glenister's Home Secretary hovers.

But Harry's certainty that a death is a murder, against the official record, is the engine here, and the show runs it hard. The Basel meeting gives the conspiracy a shape without giving it away. The hour works because suspicion is more interesting than proof, and Ros walks into the danger with her eyes open. There are quieter ways to spend an hour, but few as watchable.