Episode 6

Intelligence has it that a terrorist is planning an attack from inside his prison cell, and the man orchestrating it is an Algerian militant whose reach clearly extends past the walls. MI5's response is the sort of decision that sounds sensible in a briefing room and terrifying everywhere else. They let him out. Free him, on purpose, and hope that the freedom buys them the information they need about his plans and his network.

The release starts a manhunt in reverse. The team has to watch a man they chose to set loose, read who he talks to and where he goes, and piece together a conspiracy that was supposed to stay contained behind institutional walls. Jimi Mistry's Nazim Malik sits at the centre of it, and Joanna Roth's Rebecca Sinclair orbits him with an agenda of her own. Every move the watchers make feels like a bet.

It is the kind of gamble the show handles better than almost anyone. The logic is clean: better to know where the bomb is than to hold the man who might have built it. The trouble is that the logic belongs to a committee and the consequences belong to the city. Spooks has never been shy about that gap, and the hour leans into it.

David Farr and David Wolstencroft wrote the episode, Jeremy Lovering directed it. Peter Firth's Harry owns the decision, with Anna Chancellor's Juliet, Rupert Penry-Jones's Adam, Olga Sosnovska's Fiona, Miranda Raison's Jo Portman, Raza Jaffrey's Zaf, Hugh Simon's Malcolm Wynn-Jones and Debra Gillett's Debra Langham working the fallout.

And the hour keeps asking whether freeing a dangerous man is a clever trick or a slow-motion mistake, without ever making the answer easy. Sometimes the right call and the safe call are different things, and the episode does not pretend they are the same. That, more than the plot, is what stays with you.