When charismatic terrorist Adam Qasim escapes from MI5 custody during a routine handover, the Head of Counter Terrorism, Sir Harry Pearce (Peter Firth) - is blamed. Disgraced and forced to resign, no-one's surprised when Harry disappears one night off a bridge into the Thames...

With MI5 on its knees in the wake of the Qasim debacle and facing controversial reform, former officer Will Holloway (Kit Harington) is brought back to uncover the truth they feared - Harry's still alive. He's gone rogue, and needs Will's help.

As Qasim prepares his devastating attack on the heart of MI5 in London, Will must decide whether to turn Harry in - or risk everything by trusting the damaged, dangerous master spy who has already betrayed him once before...