On the Trail of the Mountains' Mysteries - Lynne Armstrong-Jones - Bog

The On the Trail adventures continue in book four ...
What seemed like a straightforward mission becomes an eerie mystery. All the king had ordered them to do was to follow the old map through the Noble Mountains to ensure its accuracy. It should have been a routine undertaking.
But confusion builds as the practitioners of magic Veras, Creda, Xyron, and Giever, with the escort Ferren, Joul, Nico, and Aldred, find themselves in an area with its own unfamiliar and sinister sorcery. As they progress through challenges, Creda realizes that her own powers are changing, and their predicament might even be her fault.
Worst of all, they begin to see that this sinister magic might be deliberately hindering their progress . . . and intending them harm. If they can't find some way of dealing with the constant, continuing dangers from the mystical surroundings, the entire kingdom could be threatened.