Following his visit to M. de Tréville, d'Artagnan takes a long, reflective walk home, completely captivated by thoughts of Madame Bonacieux. He views her as a romantic ideal—beautiful, mysterious, and uniquely privy to dangerous court secrets. He envisions receiving love notes, gold chains, or diamonds from her, mirroring the easy morality of the era where young soldiers routinely accepted lavish gifts from their mistresses. D'Artagnan approaches love in Paris like a military campaign, considering the city's wealthy women as prizes to be won. He imagines introducing the charming Constance to his fellow musketeers and hosting lively group dinners, totally forgetting his promise to rescue her imprisoned husband from the Bastille.
As eleven o'clock strikes, d'Artagnan finds himself near Aramis’s residence. He decides to stop by to explain why Planchet had summoned him earlier that day, and to eagerly boast of his new conquest. While approaching the house hidden beneath sycamores and clematis, he spots a cloaked woman hesitantly counting the windows. She approaches Aramis's shutter and knocks three times. D'Artagnan hides in a dark stone niche, assuming his hypocritical friend is entertaining a secret lover. When the shutter cracks open, d'Artagnan creeps closer to peer inside. To his utter shock, the person speaking from within the dark room is another woman, not Aramis. The nocturnal visitor pulls a distinctive white handkerchief from her pocket to show the woman inside, who then exchanges it for a second handkerchief before the shutter closes. As the visitor turns away, d'Artagnan recognizes her as Constance Bonacieux.
Consumed by jealousy, d'Artagnan follows her, accidentally terrifying the young woman. Constance collapses in fear, but cries out with joy upon recognizing her savior. She claims she has never heard of Aramis and was simply delivering a secret message to the woman lodging there. Refusing to disclose her business, she accepts d'Artagnan’s escort under a gentleman's oath that he will leave her at her destination without spying. They walk arm-in-arm to the Rue de La Harpe, where Constance stops at a hidden door.
D'Artagnan passionately confesses his love, but Constance warns him that his persistent curiosity is incredibly dangerous. When d'Artagnan reveals that he recognizes the "C.B." monogram on her embroidered handkerchief—noting it matches a token that nearly caused a duel with Aramis and could stand for Camille de Bois-Tracy—Constance trembles with fear. She implores him to abandon his inquiries for his own safety, stating that knowing her carries the threat of imprisonment or death. As midnight strikes, she begs him on his honor as a soldier to depart. Bound by his promise, d'Artagnan reluctantly bids her farewell and ardently kisses her hand as she knocks on the door, deeply entangled in the perilous court intrigue.