During a handover to the head of counter-terrorism of MI5 Harry Pearce, terrorist Adam Qasim escapes from MI5 custody. When Harry disappears soon after, his protégé Will Crombie is tasked with finding out what happened as an impending attack on London looms. Crombie eventually uncovers a deadly conspiracy.
When a terrorist escapes custody during a routine handover, Will Holloway must team with disgraced MI5 Intelligence Chief Harry Pearce to track him down before an imminent terrorist attack on London.