Episode 3

A red flash comes in: radioactive material has been detected at an airport, and MI5's intelligence says a dangerous anarchist with a taste for dirty bombs has slipped into the country. The clock starts ticking immediately, and the episode does not let it stop. For once the alarm is not a drill, and everyone in the room knows it. That the material was found at all means someone was careless, and carelessness is what the Service fears most.

The team has one lead, and it is a thin one. The anarchist's only known contact is his sister, Natalie, and so Dimitri Levendis is asked to do the oldest job in the spy's book, a honeytrap. The oldest and usually the grubbiest, and the sort of assignment that leaves marks. It sits badly with him, and the episode does not pretend otherwise. Getting close to Natalie means getting close to the brother, and the line between the operation and the woman blurs in ways that feel properly uncomfortable. Max Brown does good work with the moral mess of it, and the show has never pretended the trade is clean.

The endgame is tense and potentially lethal, which for this show means exactly what you would hope, and the episode trusts its characters to carry the finish. Sean Cook, David Wolstencroft and Jonathan Brackley wrote it, Julian Holmes directed. Peter Firth's Harry and Nicola Walker's Ruth hold the centre, with Max Brown's Dimitri out front, Lara Pulver's Erin and Geoffrey Streatfeild's Calum in the Grid, and 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 around the edges.

It is the episode that takes Dimitri out of the ensemble and puts him through the wringer on his own, and Max Brown is more than up to it. And the show makes sure it hurts.