Barcelona, 1650 - In a large inn in the city, officers returning from Flanders are noisily celebrating one of their own, Don Caesar de Bazan (Gino Cervi), "the most heroic soldier in Spain". Upstairs in the same inn, in a private room, conspirators are preparing the insurrection of Catalonia. Their leader, the Viscount de Beaumont (Enrico Glori), French ambassador to Spain, announces the arrival of powder and weapons supplied by France, but he also proposes a more subtle plan: to kidnap the King of Spain, who has been lured out of court by a female baiter (Anneliese Uhlig). Meanwhile, Don César provokes a quarrel with soldiers of the garrison, by taking the defense of a young valet. Arrived in the meantime, Renée Duras (the young woman implied in the plot), also takes the defense of the boy, but the intervention of the Viscount of Beaumont makes it possible to bring back the calm. Don César recognizes in the latter a valiant adversary during the campaign of Flanders, and the Vicomte informs him that in Spain duels are henceforth punished by death. In the evening, Don César is joined by his valet (Paolo Stoppa) who tells him that he has discovered by "inadvertence" that the barrels of Champagne wine, embarked in the ship which brought them back from Flanders, contain in fact gunpowder.