Episode 4

Abdul Kharami is an Algerian extremist under constant surveillance, and he still manages to slip his watchers. The fear is that he is ready to stage an attack on US businesses in the UK, possibly with local Iranian help. Stopping him would normally be straightforward, but the Americans recently set the team up in the Tehran explosion, and cooperation with them is fraught, to put it mildly. Ros, for one, thinks they should simply ignore him.

Harry Pearce thinks otherwise. He brings Bob Hogan up to date and authorises Operation Zebra, which is MI5's plan to infiltrate the CIA, and the suspicion runs both ways from there. Nobody on the American side is telling the whole truth either, and the team knows it. But when Kharami's plan is traced to the Iranian Special Consul, Adam Carter uses his special contact inside the consulate to find out what is going on, and it goes horribly wrong for him.

Ros, meanwhile, hears from her Yalta contacts that Kharami's intentions and his target are not what MI5 assumed. The whole operation has been chasing a version of events that somebody, somewhere, wanted them to believe, and the episode enjoys letting the audience watch the team catch up with that realisation in real time.

David Farr and David Wolstencroft wrote it, Charles Beeson directed. Peter Firth's Harry Pearce and Hermione Norris's Ros Myers carry the argument at the centre of the episode, with Rupert Penry-Jones's Adam Carter, Miranda Raison's Jo Portman, Gemma Jones's Connie James and Hugh Simon's Malcolm Wynn-Jones around them. Aykut Hilmi plays Abdul Kharami, Ofo Uhiara is Michael Johnson, Anthony Ofoegbu is Belhadj and Richard Betts is the operator.

The pleasure of the hour is watching institutional panic do the work the enemy never has to. Everyone is so busy assuming the worst of each other that the actual threat moves through the gaps. The failure here is trust itself, and everyone is guilty of it. For an episode about a bomber, it spends remarkably little time on the bomb, which is exactly right.