The curse of the Gloamglozer - Paul Stewart

In the floating city of Sanctaphrax, fusty old professors scheme and bicker with each other as they study the weather in minute detail - mistshifting, fogprobing, researching the air blowing in from beyond the Edge. But some experiments are best left alone...

Quint is the son of a sky pirate captain. He arrives in Sanctaphrax at the request of Linius Pallitax, the Most High Academe, who needs an apprentice he can trust to carry out a series of highly important tasks. Just how important, Quint is about to find out as he and Linius's only daughter, Maris, are plunged into the midst of a terrifying adventure that takes them deep within the rock upon which Sanctaphrax is built.