timespace coordinates: In the 26th century, humanity has left an overpopulated Earth to colonize a new solar system. The central planets formed the Alliance and won a war against the outer planet Independents—those who resisted joining the Alliance.
It is a continuation of Whedon’s short-lived 2002 Fox television series Firefly and stars the same cast, taking place after the events of the final episode. Set in 2517, Serenity is the story of the captain and crew of Serenity, a “Firefly-class” spaceship. The captain and first mate are veterans of the Unification War, having fought on the losing Independent side against the Alliance. Their lives of smuggling and cargo-running are interrupted by a psychic passenger who harbors a dangerous secret. (wiki)