This book tells a true detective story set mainly in Elizabethan London during the years of cold war just before the Armada of 1588. The mystery is the identity of a spy working in a foreign embassy to frustrate Catholic conspiracy and propaganda aimed at the overthrow of Queen Elizabeth and her government.

The suspects in the case are the inmates of the house, an old building in the warren of streets and gardens between Fleet Street and the Thames. These include the ambassador, a civilized Frenchman, his wife, his daughter, his secretary, his clerk and his priest, the tutor, the chef, the butler, and the concierge. They also include a runaway friar, the Neapolitan philosopher, poet, and comedian Giordano Bruno, who wrote masterpieces of Italian literature, who was later burned in Rome for his anti-papal opinions, and who has been revered in Italy for his honorable and heroic resistance to papal authority. Others in the cast are Queen Elizabeth, her formidable secretary of state Sir Francis Walsingham, and King Henry III of France; poets, courtiers, and scholars; statesmen, conspirators, go-betweens, and stool-pigeons. When not in London, the action takes place in Paris and Oxford; a good deal of it happens on the river Thames. The hero or villain, who calls himself Fagot, does his work most effectively, is not found out, and disappears.

In the first part of the book these events are narrated. In the second the spy is identified and his story put together. John Bossy's brilliant research, backed by his forensic and literary skills, solves a centuries-old mystery. His book makes a major contribution to the political and intellectual history of the wars of religion in Europe and to the domestic history of Elizabethan England. Not least, it is compelling reading.