Twenty Years After" is a historical novel by Alexandre Dumas, serving as the sequel to "The Three Musketeers." Set in 17th-century France during the Fronde, it continues the adventures of the musketeers, particularly d'Artagnan, Athos, Porthos, and Aramis. The story explores themes of loyalty, friendship, honor, and the changing political landscape of France during a turbulent period. D'Artagnan, now a lieutenant in the King's Musketeers, reunites with his old friends, and they become embroiled in political conspiracies, power struggles, and battles. The novel is known for its swashbuckling action, memorable characters, and complex plot, making it a classic of adventure and historical fiction.