A brief list of famous books with obscure sequels. Oh, and, you know, SPOILERS and such.
1. CATCH-22/CLOSING TIME by Joseph Heller
Joseph Heller's famous World War Two satire, Catch-22 follows Captain Yossarian and a large cast of characters through the horrors and absurdities of the war and each other's personalities and ambitions. A scathing criticism of bureaucratic and military hypocrisy set in a time and place of loss and tragedy, Catch-22 is loaded with dark humor.
Closing Time is about the darkness at the end of the tunnel. Taking place 50 years after the end of Catch-22, the characters are all in their late 60s or older, and, as opposed to dealing with the possibility of an untimely death, they have to deal with the inevitability of a timely one.
2. Huckleberry Finn/Tom Sawyer Detective/Tom Sawyer Abroad by Mark Twain
Mark Twain's The Adventures of Huckleberry Finn is one of the greatest pieces of American literature, and the sequel his The Adventures of Tom Sawyer. It tells the story of a young boy running from home with an escaped slave and discovering his own sense of morality and identity.
As the title of Tom Sawyer, Detective suggests, Tom and Huck are parodying the detective genre in an attempt to solve a murder. In Tom Sawyer Abroad, Tom, Huck, and Jim are kidnapped by a mad scientist and brought to Africa. These novels have largely been overlooked because they have nowhere near the depth of The Adventures of Tom Sawyer/Huckleberry Finn.
3. The Three Musketeers/Twenty Years After/The Vicomte of Bragelonne by Alexandre Dumas
Alexandre Dumas's The Three Musketeers is a historical novel, recounting the brave deeds and adventures of d'Artagnan as he joins the a unit of musketeers and becomes close friends with the mysterious Porthos, Athos and Aramis. Together, they foil plots by the evil cardinal and others.
Twenty Years After takes place twenty years after the events in the first novel. D'Artagnan is still employed as a musketeer, and must, in the course of political intrigue, recruit the help of his friends, who had retaken their lives of nobility since the end of the first book. About ten years after that, d'Artagnan becomes Captain of the King's Musketeer's and once again, he and his friends are caught in the middle of political intrigue, surrounding the rise of Louis XIV and the mysterious man in the iron mask.
4. The Witches of Eastwick/The Widows of Eastwick by John Updike
John Updike's novel is about three small town women who, as a result of being left by their husbands, become adept at witchcraft. Things go well until a devil-like figure appears and seduces them.
In the three decades since the end of The Witches of Eastwick, the main characters had all moved from the town and gotten married. But as they are widowed one after the other, they move back to Eastwick and reconnect.
5. All Quiet on the Western Front/The Road Back by Erich Maria Remarque
All Quiet on the Western Front is a novel about the horrors of war and the alienation it causes, told from the perspective of a young German soldier fighting in World War One.
The Road Back tells the story of soldiers coming back from the war, only to find a world that they cannot connect with. Only one major character, Tjaden, appears in both novels.
6. Trainspotting/Porno by Irvine Welsh
Trainspotting is about a group of heroin addicts and their friends in late '80s Scotland. A portrait of drug and punk subcultures, in a variety of local dialects, Trainspotting was longlisted for the Booker prize.
Ten years after the events in Trainspotting, the characters' lives cross paths again, connected not by heroin addiction but by involvement in the porn industry.