Episode 4

The search for the last missing person was running out of road, and then a fresh lead turns up. Hope, of the sort that had been packed away, gets pulled back out. The twist this week is that the bomber knows Lana now. She has a face and a name, and he has both. Every door she opens could be the one he wired, and every move she makes has to be weighed against what he might have set up for her. The freedom she used to take for granted has a price tag on it now.

That changes her behaviour in subtle ways. Lana has to be more careful, more calculating, and the episode watches her adjust in real time, second-guessing routes and crowds, the ordinary choices that used to come free. Daniel Brierley and Fflur Dafydd's script is interested in the cost of that caution, the way prolonged paranoia wears people down, and director Audrey Cooke gives the actors room to show the wear.

The search itself still matters, and the fresh lead carries the mystery forward, but the manhunt and the personal threat now run on the same clock. The cast keeps the balance. Vicky McClure heads it as Lana, with Emma Amos's Anya Wyles, Maisie Ayres's Wren Cheshire, Kaye Brown's Jo Adeyemi, Sam Crane's Anders Larsson, Kevin Eldon's Jeff, Jason Flemyng's Steven Wyles, Nabil Elouahabi's Hassan Rahim, Gabriella Fortuna's Jessica Tanbury and Jermaine Dominique's site manager filling out the ranks, and every one of them knows the clock is moving.

But it is a good balance: relentless mystery, quiet vulnerability. The show has never been shy about putting its people through it, but here the bruises are mostly internal. You end the hour worried about Lana in a way the louder episodes never quite manage, and that worry is the point of the whole season's slow build.