Freedom and Necessity is a deep and twisting growth of plots, intrigues, violence, death and love taking place in Britain during the 1850's and vaguely involved with the Chartist uprising: Marx and Engels (the philosophers) are actually characters in the novel. It is effective in the novel, but someone more acquainted with history than myself may find it to be gauche.
The gimmick of the storytelling (the letters), tends to destroy some of the reader's involvement with the plot: hearing someone talk about what happened is entirely different than observing it while it is happening. The authors repair this with another gimmick: one of the principle characters is gifted with an unusually exact memory so she can report occurances verbatim. In all, this is a violation of the literary principle of "show, don't tell", and it means that some sections of the novel are a bit dull.
I think the rest more than makes up for this, however, and I liked this quote from the back of the book so I am sharing it:
And so the adventure begins . . . leading the reader through every corner of mid-nineteenth-century Britain, from the parlors of the elite to the dens of the underclass. Not since Wilkie Collins or Sir Arthur Conan Doyle has there been such a profusion of guns, swordfights, family intrigues, women dressed as men, occult societies, philosophical discussion, and, of course, passionate romance.
If you like that sort of thing, give this book a try.