From audible.com:

The Serenity lands on the remote moon of Abel for a lucrative job but becomes embroiled in a young woman’s quest for vengeance and a starving frontier town’s fight for survival. Join Mal and the gang in this enthralling original tie-in novel from the award-winning series.

The Serenity crew head to Yell City, one of the settlements on Abel, a moon in the Rim. Their job: track down the killers of a local lawyer shot dead in the streets by a local gang. Their client is Annie Roberts, the eighteen-year-old daughter of the murdered man.

Lucky for them, Annie Roberts is more than capable of handling herself. Unlucky for them, the job is lot more complicated than they at first think it is. Annie’s father is not just the victim of local gang violence but also the target of some powerful men.

Taking down a local gang is one thing, but cleaning up a whole city? That’s not a job for the Serenity crew. But when their ship is impounded and Mal and the crew find themselves trapped in Yell City, they realize they are already in deeper than they could have ever imagined.