Stewart, Paul & Chris Riddell. The last of the Sky Pirates.

Stewart, Paul & Chris Riddell. The last of the Sky Pirates [Edge Chronicles #5]. David Fickling, 2005
We return to the world of the Edge about 50 years after the last book. Now the academics are driven underground and live the sewers with their huge library. Periodically they choose a group of Knight elect librarians to go out to the Deepwoods and study an aspect of life there to write their thesis. It is a surprise to everyone when Rook was one of the three chosen this time. He and his two other partners take a long journey through many perils involving many interesting characters to reach the Deepwoods where they struggle to survive and write their thesis. While there Rook runs into the last of the Sky Pirates and gets involved in his adventure. This 369 page book is full of adventure, excitement, and interesting creatures as the previous books. It carries on the series while branching out into another story line, thus keeping it fresh.