http://www.rottentomatoes.com/m/serenity/

A band of renegades on the run in outer space get in more hot water
than they anticipated in this sci-fi action-adventure adapted from the
television series Firefly. In the 26th century, the galaxy has been
colonized by a military force known as the Alliance, but its leadership
has not gone unquestioned. The Alliance was once challenged by a league
of rebels known as the Independents, but the Alliance emerged
victorious after a brutal civil war, with the surviving Independents
scattering around the galaxy. Also wandering the edges of the galaxy
are the Reavers, who have won few allies due to their violent behavior
and habit of ripping apart their enemies and eating them before they're
dead. Capt. Malcolm "Mal" Reynolds (Nathan Fillion), who fought as an
Independent in the galactic war, is the head of Serenity, a rogue
frieghter ship whose crew includes Mal's first mate, Zoe (Gina Torres),
who fought alongside him in the war, her husband, hotshot pilot Wash
(Alan Tudyk), sunny but dependable mechanic Kaylee (Jewel Staite), and
hard-nosed gunman Jayne (Adam Baldwin). The crew of Serenity wander the
galaxy, taking on whatever work they can get, from criminal activities
like smuggling and stealing to legitimately offering transport to
travelers. Passengers aboard Serenity include professional "companion"
Inara (Morena Baccarin) and holy man Shepherd Book (Ron Glass), but the
real trouble aboard the ship comes with the arrival of Simon (Sean
Maher) and his teenage sister, River Tam (Summer Glau). In time, the
crew discovers that River has remarkable psychic powers and was being
held captive by Alliance forces until Simon came to her rescue. Now the
Alliance is hot on the heels of Serenity and its passengers, with The
Operative (Chiwetel Ejiofor), a sinister Alliance tracker, leading the
chase. Serenity was written and directed by Joss Whedon (in his
directorial debut), creator of Firefly, which only lasted 11 weeks on
the air but gained a powerful cult following who rallied to get the
show released on DVD after its cancellation, leading to impressive
home-video sales and and an eventual motion picture deal. A couple of
months prior to Serenity's theatrical release, reruns of Firefly were
picked up by the Sci-Fi channel, adding even more fans to its cult
following. ~ Mark Deming, All Movie Guide