In the novel, the literary father of the famous captain Alatriste immerses us in the troubled pre-revolutionary times of French history at the end of the 18th century. The old world is collapsing, French prisons are overcrowded, books are being burned, terror is intensifying. And against this alarming background, Don Ermogenes Molina, an academician, translator of Virgil, and his comrade, the retired commander of a brigade of marines, Don Pedro Zarate, on instructions from the Royal Spanish Academy, go to Paris in search of the first edition of the disgraced “Encyclopedia” of Diderot and D'Alembert, which The Holy Inquisition included it in its “Index of Prohibited Books.” The expedition of two Spaniards could result in their death at any moment, because they are not the only ones hunting for book rarities. And yet, the shadow of the guillotine hangs invisibly over them...