Broadway.com has a thorough, and very enjoyable, article about The Mystery of Edwin Drood and its many incarnations through the years, culminating in the current Broadway revival of Rupert Holmes's musical version.
And Playbill.com has an interview with Holmes himself, which explains just what a mammoth undertaking the musical is. (You may recall that the show is staged as a play-within-a-play, and the audience is allowed to vote on the outcome.) Here's a quote from the latter article:
"There are eight candidates for murderer, five candidates for the detective-in-disguise and 36 combinations of lovers. If you combine all the different components, all the different lines that everyone has to memorize, there are over 400 permutations of endings — some combinations of which I have never seen. That does not mean I sat down and wrote 400 endings, but there are 400 combinations of different characters being different things. Each actor has to be responsible for what he would do if voted a detective-in-disguise or a murderer or a lover. The women have to know what they will say to nine or ten potential lovers so that it all makes sense. To be a swing on this show is to earn the Congressional Medal of Honor."