Dan Simmons can scare the crap out of you. He's done it time after time with a wildly diverse range of topics from an Indian death goddess, to time traveling robots, to Inuit myths and finally in Drood we have Charles Dickens imagination!
In this novel Simmons uses real events from the life of Charles Dickens including his friend and fellow novelist Wilkie Collins to tell a chilling tale. In 1865 Charles Dickens is on a train that crashes killing many of the passengers. While attempting to assist some of the survivors he notices a tall figure moving between the survivors apparently murdering them. Dickens becomes obsessed with finding this stranger and enlists his friend Wilkie Collins to help him. Such begins a Sherlock Holmes trope with Dickens as Holmes and Collins as Watson as they attempt to track down the mysterious figure Drood.
However to dismiss this book as a Sherlock Holmes knock off would be a mistake. Simmons does a masterful job spinning a tale that is historically accurate and could have easily happened.
The central crux of the book is whether or not Drood truly exists. Is he a figment of Dickens imagination, the criminal master mind of London's undertown or Charles Dickens himself. All of the clues to figure out the mystery are there but it will keep you guessing until the last page.