Episode 5

New evidence lands that puts CIA agent Jim Coaver at the heart of the recent attacks on MI5, and Harry Pearce decides to do something about it that no one would ever put in a memo: he kidnaps him. Jim Coaver is an old colleague, a Cold War acquaintance, and snatching him off the street is the kind of move that would end most careers. It does not end this one. Whatever else you say about Harry Pearce, you cannot say he hesitates.

The trouble is, the evidence starts to wobble. The longer Harry holds Coaver, the more he suspects he has been looking in the wrong place, and that the man sitting in front of him might be innocent. Kidnapping a man is one thing; admitting you were wrong about him is another. The episode turns on that doubt. The second half is an infiltration: Harry and Ruth need to get into the US embassy and steal Coaver's laptop from under the noses of the Americans. It is exactly as tense as it sounds, and twice as awkward diplomatically. Embassy work is about manners as much as lies, and the episode enjoys the difference.

Bharat Nalluri directed, and he keeps the whole thing moving without letting it become noise. Peter Firth's Harry is at his most stubborn and most vulnerable here, and Nicola Walker's Ruth is the one who keeps the whole thing from collapsing. Max Brown's Dimitri, Lara Pulver's Erin, Geoffrey Streatfeild's Calum, Tom Weston-Jones's Sasha, Alice Krige's Elena, Jonathan Hyde's Ilya, Simon Russell Beale's William Towers and William Hope's Jim Coaver complete the cast.

It is a duel, not a shootout, and the show is smart enough to play it that way. The embassy scenes give the episode a different texture from the Grid-bound hours around it. And watching Harry realise he may have kidnapped an innocent man is more gripping than any firefight.