The Stone Pilot by Chris Riddell

Age :7-11

An exclusive story, tracing the history of Maugin the Stone Pilot, who Twig meets in STORMCHASER. Maugin is a termagent trog, destined to change from a beautiful delicate creature into the fearsomely impressive adult termagant at her first blooding, due very soon. But an ill-fated trip above ground to release her prowlgrin pet into the wild ends with her capture by mercenary Deepwoods slavers. Maugin's subsequent sale to a terrifying scientist - for use in some kind of macabre experiment - could be the end of her - but for the actions of a young sky pirate, Quint Verginix. When Quint takes her on board his father Wind Jackal's skyship, Maugin experiences a world a million miles away from her underground home and begins a new future as a Stone Pilot.
A wonderful accompaniment to the series and a must for any Edge Chronicles fan. Told in the first person, we finally discover how the delicate young trog came to be so far from home.