Firefly was a short-lived sci-fi/western series on the Fox network. A great ensemble show, it featured a motley collection of characters on the edge of society just trying to get by. As opposed to the clean and prosperous Star Trek world, this series was set in the nitty-gritty world of folks on the edge of the law.
The premise of Firefly is that humanity used up earth's resources and was forced to settle in a new solar system with dozens of planets and even more moons. The story is set after a bloody civil war between the powerful Alliance, a fascist group seeking to unite all the planets under one rule, and the Independents, those who sought to rule themselves.
Serenity, a Firefly-class ship (full of lots of hidden compartments for smuggling), has a crew including the captain and his first mate, Mal and Zoe (two war vets who fought for the Independents, or Browncoats); Wash, a pilot of amazing skill (and Zoe's husband); an adorable genius mechanic, Kaylee, and their hired gun Jayne. A registered companion (a highly respected and completely legal call girl) Inara, rents one of the shuttles. The passengers include Simon and River, a fugitive doctor and his gifted but disturbed sister, and Book, a preacher who has a mysterious past.
Serenity takes Firefly to the big screen. It stands alone as a movie, though if you've seen the series, you'll have a better idea of the setting an the relationships. In the movie we find out more about what happened to River, a 17 yr. old genius and psychic. We also find out about the origins of the Reavers, the violent and cannibalistic marauders at the edge of the solar system.