After a bomb destroys their flat, Esther Brookstone, ex-MI6 spy and ex-Scotland Yard Inspector in the Art and Antiques Division, and Bastiann van Coevorden, her husband, ex-Interpol agent, and current MI5 consultant, are forced to stay in an MI5 safehouse along with others who are threatened by the bomber and his accomplices. The hunt for the domestic terrorists is UK- and EU-wide and leads to the discovery of a nationwide conspiracy, all financed by the far right and designed to purge the UK of perceived invaders, migrants and refugees who are accused of wanting to "replace" the white majority.