Answer:
According to the back of the book the three Musketeers at the back of the book it says that's Athos, Porthos and Aramis along with a forth person is sent to Paris to help bodyguard King Louis XIII when the tale turns for the worst.
It then goes on to say that Dumas (the author) breathed fresh life into the genre of historic romance, creating a vividly realized cast of characters and a stirring dramatic narrative.
I think that those are the names of the three musketeers. I've read the fist few pages with no luck, sorry about that. Good luck anyway!
Hope I helped!
Athos, Porthos, D'Aramis and D'Artanion. yeah I know that makes four but that's the way the book is written.