The Three Musketeers is the first in Dumas's celebrated D'Artagnan trilogy, which includes Twenty Years After (Vingt Ans Apres) and Ten Years Later (Dix Ans Plus Tard). This last book is the most famous of the sequels, as it includes the volume published in English as The Man in the Iron Mask. All three books follow the adventures of D'Artagnan, and his friends Athos (the melancholy aristocrat), Porthos (a worldly bon-vivant), and Aramis (a poet, later priest, and ladies-man). The Three Musketeers chronicles D'Artagnan as he arrives in Paris, dreaming of one day becoming a musketeer, and his exploits at saving the queen from the nefarious plotting of Cardinal Richlieu and the beautiful spy Milady.
Tous Pour Un, as a title, is the first part of the infamous musketeers' motto, which first appears Chapter IX of the text:
"Et maintenant, Messieurs," dit d'Artagnan sans se donner la peine d'expliquer sa conduite à Porthos, "tous pour un, un pour tous, c'est notre devise, n'est-ce pas ?"
"And now, sirs," said D'Artagnan without taking the troble to explain his conduct to Porthos, "All for one and one for all, that's our device, is it not?"