Detective Inspector Balvinda Smith-Kaur is transferred from the West Midlands Police Force to the Metropolitan Police. She is to set up a team to investigate the wholesale massacre of prominent politicians and industrialists just weeks before at a meeting they were holding at a venue called Heybrook Hall. Initial investigation by MI6 and Special Branch concluded that the killings were carried out by a radicalised lone suicide bomber with links to Islamic State.
However, as a senior police officer was also killed, the newly appointed Metropolitan Deputy Commissioner is far from happy with the investigation carried out jointly by SO15 and MI5. The Deputy Commissioner feels that there is more to the massacre than a simple suicide bombing and wants a deep forensic investigation carried out. Detective Inspector Balvinda Smith-Kaur is given the task of setting up a team to investigate the massacre and the supposedly unrelated death of three other police officers, who died in tragic circumstances shortly after the killings at Heybrook Hall. But the team she sets up find more than they had bargained for and soon they become the hunted themselves!