Episode 3

Zoe goes into the Turkish Embassy to check the bugs and walks into a siege. The men holding the place want their parents released from prison, and they are not in a mood to negotiate slowly. For Zoe the danger is doubled: if anyone works out she is a PR consultant in name only, she is dead. The episode doesn't let her forget it, and neither does it let her sit still.

Outside, the team does what it can, which is less than it would like. Then Harry says the thing nobody wants to hear: the embassy is a distraction. Whatever is really coming is bigger, and the hostage crisis is just the part that keeps everyone looking in the wrong direction. It's the classic Spooks move, taking a contained, tense situation and pulling the floor out from under it. Every minute inside the embassy counts twice, once for the hostages and once for whatever the attack was bought to hide. The hour builds its momentum quietly, and the pay-off is worth the wait.

Tessa, meanwhile, has her own shock. A man from her past walks back into her life at the worst possible moment, and Jenny Agutter plays the recognition with a stillness that says more than any line of dialogue. For Tessa it is the worst kind of surprise: the past arriving with no warning, just when her present is at its most fragile. Jeremy Bulloch, a long way from the armour that made him famous, turns up as Roger Welks to add to the chaos.

Simon Mirren and David Wolstencroft wrote the script, Rob Bailey directed. Peter Firth's Harry, Esther Hall's Ellie, Heather Cave's Maisie and Christopher Fulford's Johnny Marks all carry their share of a very busy hour.

The siege itself is tense enough to stand alone. But the reveal that it was never the real story makes it something better, and the episode earns the right to leave us waiting for the other shoe to drop.