The plot centers around Felix, a young man who has had a difficult time growing up. One night at a prestigious ball he falls in love with Madame de Morstauf or Henriette. He then goes up to her house in Toraine in a beautiful valley and spends great lengths of time with her.
Her husband is a tyrannical type of guy, prone to violent fits but Henriette is determined to stick with the marriage. Felix and her develop an odd kind of relationship, almost like brother and sister. Felix then falls in love with an Englishwoman realizing he has no chance with Henriette. Henriette dies of jealousy.
That is a very sketchy plot outline.
The book is too long and a bit boring for Balzac. His lead male charcters are always variations on the same thing and he spends far too much time dealing with atmosphere and surroundings.
As usual Balzac uses words like "ardent", "ardour" and several others far too much and in each of his novels I've noticed that all of his characters mention at one point that they are willing to sacrifice themselves for their lovers. Of course they never do.
There are many wonderful parts to this book, especially a cutting letter describing the differences between French and English women.
A very good book, but for Balzac, my favorite, this is one of the weaker ones.