MI5 are confronting an old enemy - Russia - as it emerges as a new superpower, while continuing to battle the threat of Islamist terrorism. In episode one, The Last Post, former British MI5 officer, Lucas North, was returned on a secret spy swap after having suffered eight years in a Russian gaol.

Anxious to get back onto the Grid and back to work, Lucas joined forces with MI5 officer and friend, Adam Carter, to rescue a kidnapped British soldier, just back from Afghanistan and being held by Al Qaeda terrorists. Meanwhile Ros, who had been working undercover in Russia after faking her own death, was called back to London by Harry. She provided vital intelligence to MI5 revealing that Al Qaeda, supported by Russian Chechens, planned to detonate a bomb during a London Remembrance service in protest against the war in Afghanistan.

Adam and Lucas were despatched to prevent the blast. Adam found the bomb in a car parked near the service, and heroically drove the vehicle to an empty London square where it could detonate at no risk to civilians, but tragically was himself caught in the blast and killed.