De Guiche enters. He says that he knows the cadets do not like him. The cadets continue smoking and playing cards as if they were not paying any attention to De Guiche. They do not want him to know how miserable they are. He tells them of his action in the war the day before. Cyrano, however, knows every detail. He knows that when De Guiche's life was in danger, he flung off his officer's scarf so he would not be recognized. Cyrano picked up the scarf, and now exposes De Guiche's cowardice by producing it. De Guiche mounts the parapet and waves the scarf, explaining that, with the aid of a spy, he has arranged for the Spanish to attack at the position from which he signals. At the same time, the French armies will mount their own attack against the weakest position of the Spaniards. De Guiche admits that, by ordering the attack on the Gascony Guards, he serves both the king and his own rancor.
Christian says that he would like to put his love for Roxane into one last letter. Cyrano hands him a letter he has ready. Christian notices that a tear has splashed on the letter, and Cyrano explains that the letter was so beautiful that he himself was carried away with emotion.
The sentinel announces that a carriage approaches and the cadets line up, preparing a salute.
De Guiche is certainly not a pleasant character, but he is at least honest. The attack that he has arranged for at this position will probably turn into a massacre of the Gascons. The cadets show their dislike for him quite openly, and Cyrano has shown that his own courage exceeds that of De Guiche by retrieving De Guiche's scarf from the most dangerous part of the battlefield. It is another touch of irony in the play that Cyrano's displaying of the scarf is the action that makes De Guiche come to a definite conclusion about inviting the attack.
Rostand has established that Cyrano manages to get through the lines to send letters, but at very great risk on his life. Surely, if it were at all possible to get food in, he would do so. Thus, when a coachman arrives, declaring that he is in the service of the king of France, it is certainly cause for amazement.
This business is ridiculous, but absolutely essential for the development of the plot. Rostand does it about as well as it could be done, inasmuch as he thoroughly prepares the audience for everything explainable and makes a thorough surprise of what is not logical.