The Three Musketeers - 25 rue Vaugirard

“Do you know where the duchesse de Chevreuse and the duke of Buckingham are now concealed?”
“No, monseigneur; my people could tell me nothing on that head.”
“But I know.”
“You, monseigneur?”
“Yes, or at least I guess. They were, one in the Rue Vaugirard, No. 25; the other in the Rue de la Harpe, No. 75.”

(Alexandre Dumas)

ED. The building numbers on rue de la Harpe end in the 40s.