In the future, mankind consumed planet Earth, called ``Earth-that-was``, and moved to other planets and satellites. A new order is established with the totalitarian government of the Alliance, which fights and wins a war against their opponents, the independents. When Dr. Simon rescues his teenager telepathic sister River Tam from the claws of the Alliance, they are sheltered by a group of mercenaries and smugglers in the spacecraft Serenity, leaded by the former war hero Captain Malcolm ?Mal? Reynolds. The Alliance send an assassin to bring River Tam back, while Mal and his crew find out how powerful she is and the truth about the hidden planet Miranda and the origin of the cannibals Reavers.