In this 'sequel' the characters of "Pride and Prejudice" find additional drama in their lives when a murder occurs on the Pemberley estate.
As the book opens Elizabeth Darcy, who's been happily married to Fitzwilliam Darcy for six years now, is preparing for Lady Anne's ball - an annual event at Pemberley. On the evening before the grand event a horse drawn carriage careens up to the Pemberley mansion and Elizabeth's flighty young sister Lydia emerges, screaming that her husband is dead. Turns out a hired carriage was carrying Lydia, her irresponsible, rakish husband George Wickham, and Wickham's friend Captain Denny to Pemberley when Denny demanded the driver stop the carriage. Denny then got out, hurled harsh words at Wickham, and entered the woods. Wickham, trying to stop Denny, followed him. Soon afterwards shots were heard, Lydia became hysterical, and the driver took off for Pemberley. Lydia's appearance was completely unexpected since she and Wickham were not invited to the ball and Wickham was not welcome at Pemberly under any circumstances.
Darcy organizes a search of the woods and Captain Denny is found dead with grievous wounds on his head. Wickham, beside the body, is distraught - moaning that it's his fault that Denny is dead. The authorities are notified, witnesses are questioned, there's an inquest, and Wickham is put on trial for murder.
I know some people liked this book, part of the pleasure being the opportunity to visit familiar characters including members of Elizabeth's family, and Darcy's sister Georgiana and her suitors. There are other interesting personalities in the book as well, including members of the too full-of-themselves British 'upper classes', servants in the Pemberley household, workers on the estate, an extortionist, and so on. I found the plot slow-moving and tedious, however. The story moseys along to a climax after which there's a very long section of exposition explaining everything that happened.
In my opinion this is a rare case where the the TV adaptation of the story (a three-part miniseries available on Netflix) is much better than the book. In the TV series the important plot points are distributed throughout the story, a structure that's much more compelling than having a couple of guys explain everything at the end. Plus there's more dramatic tension, which admittedly takes a little licence with the story but makes it more engaging.
All in all, not a great book.