Episode 1

Series six opens in Tehran, which is a bold place to put your opening credits. A rogue member of Iranian intelligence may be planning to unleash a bio-weapon in the UK, and Zafar Younis and Adam Carter are sent in to stop it. The mission goes wrong from the start, and the farther they get from home, the less anything resembles the briefing.

As the investigation moves forward, it becomes clear that the two of them were deliberately misled about what the assignment was actually for. That double layer is the engine of the hour. The team chase a threat on the ground while slowly realising that the people who sent them have their own reasons, and every new revelation of deception forces them to adapt on the move, in a city where they have no friends and no fallback. It is a tightly wound way to begin a run, and it sets a sour, suspicious tone that suits the season.

The episode also makes room for the people back home. Harry Pearce watches from London, and the distance between him and his officers in Tehran is part of the point; he cannot help them, and he does not fully know what they are walking into. There is jeopardy in the mission and in the office, which is the show's favourite double trick.

Neil Cross and David Wolstencroft wrote it, Omar Madha directed. Peter Firth's Harry Pearce is in place, with Rupert Penry-Jones's Adam Carter, Hermione Norris's Ros Myers, Raza Jaffrey's Zafar Younis, Miranda Raison's Jo Portman and Hugh Simon's Malcolm Wynn-Jones. Agni Scott's Ana Bakhshi, Matthew Marsh's Bob Hogan, Simon Abkarian's Dariush Bakhshi and Rob Marni's Ebrahim fill out the hour.

The episode works best as a warning shot. But it also promises a season in which the team cannot take its own briefings at face value, and the viewer spends the whole hour waiting for the other shoe. For an opener, you could do worse.