While Treville, is writing a new letter of introduction, d'Artagnan glances out the window and, by accident, sees the person who robbed him. He runs after him, and while pursuing him, he offends three musketeers: first, he collides with Athos, reinjuring Athos's wounded shoulder; then he jostles Porthos and reveals a partly counterfeit golden shoulder belt that he is wearing; and finally, he offends Aramis by ungallantly and unintentionally bringing attention to a lady's handkerchief. He is challenged to a duel by each of the musketeers. After he meets the musketeers and begins dueling with Athos, they are all threatened with arrest by the dreaded cardinal's guards because of a law against dueling. D'Artagnan joins forces with the musketeers and helps drive the cardinal's men away. Thus, almost immediately after his arrival in Paris, D'Artagnan becomes an intimate friend of the three musketeers.