After distinguishing himself by courageously neutralising a terrorist threat, troubled war veteran Police Sergeant David Budd 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.

Another terrorist attack raises the UK threat level to severe. Home secretary Julia Montague holds secret meetings with the director general of the security service, freezing out the police and her own minister of state for counter terrorism.

As the capital shudders in the wake of two terrorist attacks, specialist protection officer PS David Budd is more under pressure than ever to keep the home secretary Julia Montague safe. The threat to her life does nothing to curb Julia's political ambitions, as her counterterrorism bill takes another step towards being made law, provoking political rivalries.

Traumatised by the events of the last 24 hours, PS David Budd falls under suspicion. Pushed to breaking point, David is helped back on his feet by his estranged wife, Vicky, and is determined to play an active role in the investigation.

Determined to push the investigation forward, PS David Budd targets enemies of home secretary Julia Montague. As he delves into Julia's political manoeuvring before the attack, David’s theories about a conspiracy at the heart of government look increasingly plausible.

Principal Protection Officer David Budd has made a major breakthrough in the investigation into the attack on the home secretary, but his enquiries have put him in mortal danger. With the clock ticking and no-one left who believes him, David attempts to prove his innocence. But the evidence against him begins to stack up.