The Ropemaker (HB) by Peter Dickinson
The people of the Valley have been protected by powerful magic for twenty generations. No enemies from the Empire on its borders can penetrate the poisoned forests to the south or the deadly glaciers to the north. But the spell is weakening...Setting out to challenge the might of the evil Emperor and his powerful magicians are young Tilja, her three companions and an obstinate horse. They must seek a mythical figure from centuries ago - and on their long and perilous journey Tilja discovers her own strange power. It will enable her to enter the Empire's most guarded fortress, and discover the identity of the one they call the Ropemaker - a man who controls the rope of time itself...Peter Dickinson's first novel of high fantasy is a work of extraordinary inventiveness, rich and vast in its scope - creating a new and brilliant world for all readers who love the power of magic.