Episode 6

Harry Pearce is being handed to the Americans. The death of CIA agent Jim Coaver has made him a liability, and now he faces deportation to the United States, where the questions will be longer and the answers shorter. The episode opens with the Service's senior officer in CIA custody, and it does not pretend that anyone can simply ask nicely for him back. It is a long way down for the man who has run the Service for a decade, and the episode lets that sink in before it starts moving.

Then new evidence surfaces about the attacks on the UK and about the government's proposed alliance with Russia, and the picture changes. Ruth and her former colleagues in Section D take matters into their own hands and spring Harry from custody. It is a team effort, and it is nice to see the Grid working together after a season of suspicion. It is the kind of operation that looks brilliant on screen and would be a diplomatic catastrophe in real life, which has never stopped this show and should not stop you enjoying it.

Harry's suspicions do not end with his freedom. He is convinced the answers lie further back, and so he goes looking for another adversary from his Cold War days. The trail is a cold one, but Harry has never needed the trail to be warm. Jonathan Brackley, Sam Vincent and David Wolstencroft wrote it, Bharat Nalluri directed. Peter Firth is in near-constant motion as Harry, with Nicola Walker's Ruth, Max Brown's Dimitri, Lara Pulver's Erin, Geoffrey Streatfeild's Calum, 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 him.

It is a running episode, one that keeps the team in the field and off the Grid, and the pace suits it. And the sight of Harry Pearce, officially wanted, calmly walking towards the next secret is a good reminder of why he has outlasted everyone.