The crew of Serenity take on a train heist commissioned by a crime lord. They steal the goods, only to find it is medicine that's desperately needed by the town.

Serenity is pulled in by a Tohoku-class cruiser while investigating a spaceship that was attacked by Reavers. Simon and River must hide to prevent capture, while something is wrong with the lone survivor of the attacked spaceship.

After Serenity suffers a catastrophe that leaves her crew with only hours of oxygen, flashbacks show how Mal and Zoë acquired Serenity and assembled their motley band.

A former Independence soldier who had served with Mal and Zoë returns in a dramatic manner, with a vicious Alliance officer chasing after him for some unusual smuggled goods.