De Guiche enters and tells Roxane that he has come to say goodbye. He has been placed in command of Cyrano's regiment. She tells him that if he really wants to hurt Cyrano, he should leave him and the other cadets behind, while the rest of the regiment goes on to glorious victory. De Guiche sees in this a sign that Roxane loves him (De Guiche) and suggests a rendezvous at a monastery. She makes De Guiche believe she is consenting; she has managed to keep Christian out of the war.
Cyrano comes out of the house and asks Roxane on what subject she will ask Christian to speak tonight. She replies that tonight he must improvise on the subject of love.
For the sake of Christian, Roxane plays the coquette with De Guiche, and very skillfully. We are shown how powerful De Guiche is, and how much vengeance he would take for a slight, for Cyrano has only refused De Guiche's offer to be his patron. He does not hesitate to use this threat of revenge against Cyrano (and Christian, too, though he does not know about Christian's relationship with Roxane) to influence Roxane.
When Roxane tells Cyrano that Christian's subject for the evening will be to improvise on love, he sees an opportunity to work in all the beautiful phrases he has been saving up for just such an occasion.