After distinguishing himself by courageously neutralising a terrorist threat, troubled war veteran Police Sergeant David Budd (Richard Madden) of the Metropolitan Police's Royalty and Specialist Protection Branch (RaSP) is assigned as a Principal Protection Officer to the Home Secretary, the Rt. Hon. Julia Montague, MP (Keeley Hawes). Julia is a controversial politician intent on pushing a new counter terrorism bill through Parliament which would give the Security Service enhanced surveillance powers. Her political ambitions make Julia a high profile target. Dedicated to his job but concealing deep resentment of politicians following his traumas in Helmand, David's divided loyalties might make him Julia's greatest threat.