Emilie and the Sky World -- Martha Wells

Emilie's been back from her adventure in the Hollow World for only a short time before the uncle whose home she fled shows up with her brother to take her back.  But bigger things are in store.  Something has shown up in the aetheric current -- a ship unlike any seen before.  It can only mean that the Hollow World isn't the only one that can be reached by means of the currents.  Are the ship's occupants friendly, or to they mean trouble?  There's only one way to find out, and so it's off into the aether again for Emilie and her companions from the earlier book, along with her stowaway brother.  

When they reach the other ship, it appears to be deserted, and the first party that goes to investigate disappears.  What could have happened to them?  I'm not going to tell, but I have two words for you: ghost pirates.  If that doesn't sell you, well, you just don't think like I do.  

Let me add that there are several twists and turns to the narrative before things are settled and that there's more than just adventure going on. Emilie and her brother have a few issues, and their evolving relationship is one of the things that makes the book entertaining.  As in the first book, Emilie proves herself clever, resourceful, and ready to take risks for her friends.  If you're looking for a fast-moving YA adventure with interesting characters and a vivid setting, this is it.  Check it out.