Episode 2

Harry Pearce keeps a file on sleepers: people living ordinary lives until the service needs them. Fred Roberts is one of them. A renowned chemist and a family man, Fred is activated and sent to work his way into a terrorist group. He does what he's asked, and he does it well enough that the group takes him in. For a while it looks almost routine, the way the best operations do.

That's exactly the problem. Tom watches Fred sink deeper into the terror cell and starts asking what the service is willing to spend to get results. The group he is inside is deadly, and the deeper Fred goes, the harder it becomes for anyone to pull him out. Fred's wife Liz and daughter Sophie, played by Hannah Bridges and Rebecca Bridges, are the human cost the operation file doesn't mention. Jenny Howe's Mrs Sayle and Jalaal Hartley's Lawrence Sayle are the people around the edge of the story, ordinary lives caught in the blast radius of someone else's operation.

Richard Harrington's Will North, Shauna Macdonald's Sam Buxton, Rory MacGregor's Colin Wells and Keeley Hawes's Zoe make up the supporting team. Peter Firth is Harry, the man who lit the fuse and will not be moved. Matthew Macfadyen's Tom carries the episode's conscience. Howard Brenton and David Wolstencroft wrote it; Jonny Campbell directed.

The episode asks whether one man's life is a fair price for national security, and it doesn't pretend the answer is easy. Tom's crisis of conscience is the heart of it, the point where duty and decency stop pulling in the same direction. And the show leaves you to decide whether Fred was ever really a free man, or just a tool with a family attached. The episode trusts you to sit with that, which is rarer than it should be.