Eric Ambler 
Judgment on Deltchev [PDF ebook] 

Foster is hired to cover the trial of Deltchev, who is accused of treason for allegedly being a member of the sinister and secretive Brotherhood and preparing a plot to assassinate the head of state whilst President of the Agrarian Socialist Party and member of the Provisional Government. It is assumed to be a show trial, but when Foster encounters Madame Deltchev the plot thickens, with his and other lives in danger ….