In chapter 28, M. de Treville awards d'Artagnan the position of a Musketeer. Yet in the very first paragraph of chapter 29, d'Artagnan refers to himself as a mere guard. It is because he is not a Musketeer that he cannot go on campaign with the other Musketeers in the next few chapters. And in chapter 47, M. de Treville writes him another letter, making him a Musketeer-for the second time.