In the distant future, humans leave the overloaded Earth and continue their civilization in new galaxies. The planets in the center of those galaxies form an alliance and constantly try to bring remote and wild planets into their sphere of influence. The girl Reva (Summer Glau) is transformed into a sensitive and agile fighting machine under this policy of the alliance. Reva's brother Simon rescues her and takes her to the transport ship "Serenity" owned by Mal (Nathan Fillion), a former member of the resistance organization. On the other hand, in order to prevent the leakage of intelligence that Reva may have, the Alliance Parliament sends a vicious envoy to pursue her endlessly. Mal and his party are repeatedly in danger because Reva's combat mode is awakened by the Alliance. The crew has to go to the marginal land - Moranda with difficulty amidst the irrational cosmic predators and the Alliance's obstruction, where a sinister past that the Alliance does not want to show is buried... This film is the sequel and ending of the TV series "Firefly", and won professional praises such as the 2006 Saturn Award for Best Supporting Actress.