This scene takes place a month later in downtime from a siege, with battle drums and other war-related paraphernalia. It is near dawn.
When the action starts, we see that Cyrano’s regiment—under the command of Captain Carbon de Castel-Jaloux—is starving. Carbon calls on Cyrano to raise the men’s morale, which he does by jesting with them and turning their hunger for food into homesickness (hunger for the homeland).
Comte de Guiche arrives. The soldiers hate him for his obvious wealth and arrogance. They don’t want him to see them miserable so they pretend to be happy by playing card games and dice upon his arrival.
The Comte knows he is not popular among the soldiers, which isn’t so much a reflection of his amazing abilities of perception as much as the obvious intensity of their disdain.
De Guiche decides that, despite this hatred, he should boast about his cleverness by telling stories. Awesome.
During a siege, the Comte begins, he found himself in the enemy lines of the Spaniards. So he quickly took off his white scarf—a mark of French military rank—blended in with the other fugitives, and got away alive.
Cyrano accuses him (deftly, of course) of cowardice; if he himself had been there, he says, he would’ve taken the white scarf from the Comte, worn it to make himself a target, and displayed his manly courage.
The Comte scoffs at Cyrano. Nice comeback. The scarf is gone, he says, so Cyrano can’t prove his manly courage or whatever.
Cyrano one-ups him by producing the very same white scarf from his pocket. Oh, snap.
In revenge, Comte de Guiche tells the regiment some news of the war; his Spanish spy has reported that in order for the French army to be resupplied, this regiment will have to sacrifice themselves to the Spaniards. This way, there’s more time for the Marshal to get the supplies to the army, since the enemy (who outnumbers them 100:1) will be busy slaughtering these guys.
Christian realizes he will probably never see Roxane again. He goes to Cyrano with a heavy heart, saying he wants to write a farewell letter to his love.
Cyrano is way ahead of him; he’s already written it.
Christian notices a teardrop on the letter and questions Cyrano about it. Cyrano answers glibly that a poet often believes what he writes and is moved to tears by it.
Convincing speech, but Christian, for all his ineloquence, isn’t stupid; he begins to suspect the truth: Cyrano actually loves Roxane himself.
As all the soldiers despair, someone arrives in the King’s carriage. It's Lady Roxane. Everyone, including de Guiche, tries to tell her to go home to safety, but she will not listen.
The men are delighted to see a woman among them. They clean themselves up to meet her, and the gallant Carbon ties her handkerchief to a lance to use as the Company’s flag.
After de Guiche leaves to check on weapons, Roxane reveals that her carriage’s footman is none other than the poet-pastry chef, Ragueneau. Together, they unpack huge amounts of food for the cadets—much to the soldiers’ delight. Everyone gorges.
De Guiche returns and the soldiers hide the feast from him out of spite. De Guiche, seeing that Roxane means to stay despite the danger, vows to stay and fight—and possibly die—with the men, all in her name.
The thought of de Guiche dying pleases the men, so they decide to share the food with him. Roxane then speaks with Christian; she’s become smitten by "his" letters and has come to see him and to make a confession.
The confession is this: at first, she just thought he was hot. But now, she realizes he’s not just a hot body. You know, roughly speaking.
She adds that he would love him now even if he were ugly. (Really? Even if he had a ridiculously big nose?)
Christian is appalled.
Downhearted, he reveals everything to Cyrano. Cyrano tries to reassure him, but Christian is stubborn. He realizes that not only does Roxane truly love Cyrano, but that Cyrano loves her back as well.
Cyrano admits this is true; Christian wants him to tell Roxane the truth and then let her decide whom she really loves. He takes Cyrano to Roxane and then leaves them alone together.
Cyrano gets Roxane to confirm what she earlier claimed (that she would love the letter-writer even if he were ugly).
Then, just as he is about to reveal the truth to her, Christian gets shot in battle.
Cyrano cannot bear to tell the truth now. Instead, he lies to Christian. He tells him that the truth has been revealed to Roxane and that she still loves him (Christian).
Christian dies happy.
Roxane takes his final letter (actually written by Cyrano) from his breast and reads it. She mourns for him.
Cyrano considers himself dead along with Christian, since Roxane is mourning for the writer of the letter. His life sucks.
He then entrusts Roxane to de Guiche and tells them to find safety.
Cyrano then rushes into battle, eager to avenge Christian’s death as well as his own metaphorical demise. He takes with him the banner—with Roxane’s handkerchief attached—as he dashes into the fray.
Many Frenchmen die at the hands of the Spaniards, who outnumber them greatly.
The act ends with Cyrano fighting while singing the anthem of the Cadets—first heard in Act II, when he sang it for de Guiche.