The Mystery of Edwin Drood is Charles Dickens' last novel. As was usual for Dickens, the novel was written and published in serial instalments; Dickens died after completing only six of the projected twelve instalments, leaving the novel incomplete and the mystery unresolved.The plot revolves around the disappearance (perhaps murder) of Edwin Drood, whose fiancée Rosa Bud is an object of attraction for several other characters, including his uncle, John Jasper, and the proud Neville Landless.The solution of the mystery is actually known: Drood's uncle, John Jasper, is the murderer. Dickens had told several people whodunnit, and his friend John Forster later published a synopsis of the novel's planned conclusion bringing together various details Dickens had mentioned to him, including Edwin's fate, whodunnit, and the intended fates of other significant characters. This hasn't stopped multiple people writing their own endings, not all of them agreeing with Forster's account.
The novel provides examples of:
Abusive Parents: Helena and Neville Landless were raised first by a violently abusive stepfather, then by the obnoxious, neglectful Mr. Honeythunder.
All There in the Manual: As The Other Wiki points out, Dickens named Jasper as the murderer to at least three people (his son, his illustrator, and John Forster). He also mentioned Helena's marriage to Mr. Crsiparkle and Rosa's to Mr. Tartar.
Ambiguous Disorder: Mr. Grewgious is described as a "particularly Angular man", with an expressionless face and voice, an awkward way of moving, and an inability to show even deeply felt emotions.
Ambiguously Brown: Neville and Helena Landless come from Ceylon, and are described as having a "dark complexion", but the details of their ethnicity are not clear. In any case, they are foreign enough to prejudice Edwin, Jasper, Mrs. Crisparkle and almost the entire town against them.
The BBC version specifies that they are Indian on their mother's side and white on their father's, and casts them as Indian actors.
Anguished Declaration of Love: Jasper bursts out with one to Rosa shortly after Edwin's death. She recoils in disgust, seeing his actions as a betrayal to Edwin, but he couldn't care less.
Arranged Marriage: Rosa Bud and Mr Drood are to enter into a marriage arranged by their late fathers.
Meaningful Name: As in every Dickens novel. We have Rosa Bud, the Landless twins who are without a home, a sailor named Mr. Tartar, Mr. Crisparkle (the name suggests the words "crystal" and "sparkle", to suggest both his purity and his habit of swimming in cold water), "Stony" Durdles the gravestone carver, and the aggressive philanthropist Mr. Honeythunder. Septimus Crisparkle's given name is due to his mother having had six stillborn sons before him, which explains why she is so protective.
Mama's Boy: Mr. Crisparkle is this to his mother, although unlike most examples of this trope, it's portrayed as very endearing.
Never Found the Body: Edwin Drood's body remains unfound in the completed portion of the story; at least one continuation has him reappearing alive and well at a dramatically appropriate moment. According to Forster, Dickens' intention was that they would have Finally Found the Body, its location being a pointer to the identity of his murderer.
Parental Substitute: Mr. Grewgious, though eccentric, is a genuinely good and loving guardian to Rosa. Less so Mr. Honeythunder to the Landlesses. Then there are Jasper and Edwin, whose relationship is complicated to say the least.
Servile Snarker: Bazzard is incredibly snarky and rude at all times. His employer is such a nice guy that he lets him get away with it, since he feels that Bazzard's going through a lot of trouble just working for him.
Twin Telepathy: Helena and Neville can understand each other without a word or even a look.
Notable continuations and adaptations include:
The 'James version', published in 1873. Written by an American printer, Thomas James, who claimed he had channelled Dickens' ghost.
The Trial of John Jasper, a one-off event staged by the Dickens Fellowship in 1914, and featuring several literary luminaries, including G. K. Chesterton as the judge and George Bernard Shaw as the foreman of the jury. Played very much for laughs.
Drood, a musical adaptation with multiple possible endings, the murderer being determined in each performance by audience vote.
The D. Case, a parodic novel in which various famous fictional detectives each give their opinion on the case.
References in other fiction:
The Doctor Who episode "The Unquiet Dead", in which Charles Dickens helps the Doctor thwart an alien invasion, ends with Dickens contemplating changing the ending so that Drood's disappearance was caused by aliens; Rose is worried that they've changed history, but the Doctor isn't worried because he knows Dickens won't live to write the ending anyway.