How about taking a classic book and working in a murder mystery?
That is exactly what P.D James does in Death Comes to Pemberley.
In this story, Wickham is once again creating trouble. On the way to Pemberly, Wickham and his buddy Denny leave the chaise to head for the woodlands at night. When they are found and rescued, one is found dead in the other's arms. The rest of the story unfolds what happens to the family, Pemberly and the ensuing trial. Note to readers, it is not as simple of a murder as you might think.
James does an excellent job continuing the story line and developing the characters. Never once did I find myself feeling a disconnect between Austen's original characters and James's characters. It is a fantastic read for any Pride and Prejudice fan. Also I learned there are plans to turn this book into a movie on BBC, just in case you are a fan like I am.