Disclaimer: this book is only for very massive The Three Musketeers -geeks. I am not talking about 'I enjoyed the book and [(the movie with Michael York/Charlie Sheen)/Dogtanion and the three Muskehounds was a really nice show]'. I am talking about 'I have read the book and the sequels (possibly more than once), have spent an unreasonable amount of time hunting down and watching obscure movie-adaptation of it (including the one with David Hasselhoff let us not speak of this ever), once bought a bottle of wine just because it was called 'The White Musketeer' and still have the wrapper of that d'Artagnan chocolate-bar'-level geekery.
(Obviously I would never do any of these things. I have a friend who does. Yep. She's also writing this review. Really. I am not a weird person at all. *tries to smile reassuringly*
SEE! Nobody can prove anything. Nobody!)
Anyway...back to the book. It is not particularly...thrilling. About 2/3 of it is "d'Artagnan gets into trouble because he couldn't keep his pants on but gets quickly out of it again because he is just that awesome". No seriously...this guy has more romantic adventures than all the Musketeers in all the various adaptations put together.
And yes, this includes BBC!Aramis
(I should clarify: 2/3 of the edition I was reading: a German translation where the translator pointed out in the afterword that he heavily edited/shortened it and that he considered the sexy adventures much more interesting than the description of battles and of political stuff (which Sandras got mostly wrong anyway apparently))
The rest is mostly about work he does for Cardinal Mazarin (and whining about how much of a penny-pincher he is) and the occasional trouble he got in for reasons other than 'could not keep his pants on' (those are rare...very rare).
There is no actual red line in the book. With the exception of Mazarin there are almost no recurring characters, people appear for a few pages (if they're female d'Artagnan sleeps with them, if they're male they get angry at him for sleeping with their wives) and are never seen or even mentioned again.
For a Musketeer-geek it's still interesting to see where Dumas got his inspiration from. Though if you expect this book to be a less polished version of The Three Musketeers you will also be disappointed. In the first quarter there is some stuff that will be familiar: the very beginning is quite similar to TTM, including the scene with Rochefort (who has a different name here), Athos, Porthos and Aramis are mentioned (though only two or three times), a character that was very likely the inspiration for Constance appears and so does Milady but that's it. Not much swashbuckling adventures, no secret letters that have to be delivered...so without a strong interest for Dumas (or perhaps the time-period this was written) you will probably be bored very quickly. But if you're enough of a nerd this is just the book for you at least my friend says so.