Episode 7

The trouble begins with a name. Sugar Horse turns out to be a Russian sleeper network, held in reserve for the direst circumstances, and the West picks the worst possible week to annoy it: the US announces a missile shield for former Eastern European states, relations wobble, and two Sugar Horse agents turn up murdered. Every scrap of evidence points at Harry Pearce. He is arrested, and the questioning that follows has the flavour of people who have already decided. They are not meant to be used, and the two murders land as a message rather than an accident. It is the episode where the Russian threat stops being abstract.

Lucas heads for Moscow to see what he can learn, leaving the rest of the team to argue Harry's innocence from the Grid with their hands full. Because someone on the inside has been working against them all along. The mole kills a colleague and then needs extracting fast, and suddenly the question of who framed Harry becomes a question of who else dies before it is answered.

James Moran and Christian Spurrier wrote it, and Sam Miller directed. Peter Firth does the hard work of being accused, and Richard Armitage's Lucas carries the Moscow leg. Hermione Norris, Miranda Raison, Hugh Simon, Gemma Jones and Alex Lanipekun fill out the building, Robert Glenister's Home Secretary hovers, Robert East plays Richard Dolby, and Alan Williams is Charles Grady.

But there is something properly grim about watching Harry Pearce, of all people, behind a table answering questions. The show knows it, and it milks every minute of it. For once the paranoia is justified, which is somehow worse than when it is not. There is no comfort in being proved right when the proof is a dead colleague. It is one of those hours where the cost of the answer shows on every face.