Ranger's Apprentice #4 The Battle of Skandia by John Flanagan

My eleven year old read this book to himself.  Below is his summary:
"In the cabin in the mountains of Skandia, Will breaks free from his wormweed addiction.  Horus and Halt come look for him.  Then Evanly is captured.  A massive invasion of Temujai is coming to invade Skandia."
He loves this series!
-Borrowed from the library.
The library has this book in the "young adult" section.
Warning: swearing (dn and hll)